I've spend almost 4 years teaching kids 7-13 robotics, and I can say that at that age you are almost guaranteed to have a bad time with such an open ended challenge. Children that age are simply not capable of realizing how many small problems contribute to the overall complexity of a problem. In order to effectively teach kids problem solving or robotics, it is essential to artificially reduce the complexity of the little problems. For example on our outside robot we have the following very non-trivial problems that are not strictly related to the central problem of, find interesting stuff then investigate:

1. dirt getting in our robot and clogging it. building stuff that works well outdoors is hard.
   
2. sensing different types of soil or surface. this is an enormously complex and expensive thing to do
   
3. digging, moving dirt with a little robot is very hard. the complexity of that is crazy.
   
4. cost, as a robotics engineering student in college, It would probably cost more than 1000 dollars to have a really good robot to do what you want.
   
5. time, kids get bored fast. this kind of problem would likely take an engineer a couple days at least. kids don't focus for that long.
   
   if you wanted to come up with a different challenge that would be easier to succeed and teach with, I would go with something like the following: Cut out a bunch of pieces of construction paper, maybe 1.5 inch diameter circles. mostly brown or grey or black but a few red ones. Stick all these pieces of paper on a table in a random mess, you can even cut up the paper to look like leaves or something, and the red ones to look like ladybugs, whatever works to make the mock up yard feel more real. The idea is to build an environment that is similar to outside, but has much less "hidden" complexity to overcome. Now build a robot that drives around and has a little arm with some tape on it that it can push down on the table to pick up paper with, this way our robot doesn't have to actually dig or grasp objects, which eliminates some of the difficulty of the challenge. This robot could use a simple color sensor, which comes with every Lego NXT kit now to sense the leaf color. This eliminates most of the complexity of our sensor. By using legos we have an easier platform to work with. its not longer difficult for the kid to focus for long periods of time because it can come together faster, and its more toy like. we also have a relatively low cost option, a 400$ lego kit is an amazing deal considering it can be re-configured.
   
   here are some links to robotics kits that you might like. I highly recommend lego for a kid this age, but there are some other options if you'd prefer a toy you can learn something from as well.
   
   http://www.amazon.com/LEGO-6029291-Mindstorms-EV3-31313/dp/B00CWER3XY/ref=sr_1_1?ie=UTF8&qid=1422256562&sr=8-1&keywords=NXT&pebp=1422256562324&peasin=B00CWER3XY
   
   
   polulu 3pi robot, with the addition of a servo you could build a pretty sweet robot for the task i described above:
   https://www.pololu.com/product/1306
   https://www.pololu.com/product/1058
   
   Vex robotics. geared for much more complex robots, this would be my least favorite option for someone who is only 7.
   
   http://www.vexrobotics.com/vexiq

Zombies, HazMat guy

Edit: Dinosaur guy, just in case.

You are not their target audience with this. I know parents who immediately see the value in teaching their young kids how to follow instructions to build something (LEGO) and then there is the fact that the game also teaches basic coding logic (Scratch Studio) while also combining the coding within the projects (LEGO Mindstorms)

While Scratch Studio is basically very cheap, LEGO sets and Mindstorms can range in the hundreds of dollars versus Nintendo Labo which is $80.

I really liked Lego Mindstorms when I was a kid. It's cool because they are easy to assemble because it's just legos and the coding language was pretty simple. It's a graphical block-diagram language that's nice for kids. https://www.lego.com/en-us/mindstorms/learn-to-program

Maybe you can find it used on eBay? Or you can get Chell for 10$ http://www.amazon.com/LEGO%C2%AE-Portal-Chell-Minifigure-portal/dp/B01DCOHEBS/

I actually do know about building robots, having professionally worked as a programmer and participated in many FIRST robotics competitions.

I don't know anything about Big Hero 6, but looking it up, your son's plan isn't a viable place to start. Lego mindstorms is probably the easiest way for a beginner to get into robotics, and I think it would be a good activity for you and your son. Look at a kit like this one.
http://www.amazon.com/dp/B00CWER3XY/

You can see the basics of what it is in this youtube video.
https://www.youtube.com/watch?v=qzOza1fO9_8

There are videos of a bunch of other videos on youtube showing creations with it, if you look around.

Slightly more advanced would be getting into something like arduino programming, but that is a bit much for a five year old. Personally I think that lego is the way to go here.

If his interest holds and he wants to go a little further, FIRST even has a jr lego league for kids ages 6-9. I've only helped with mentoring high school teams for FRC, but I am sure it is still probably a lot of fun. You might see if there is a team nearby.
http://www.firstinspires.org/robotics/flljr

A good quality Boba Fett goes for about $20-$30(gun not included).

Get this Trump minifig instead. It looks far better and the people who produce it are neutral

Board games. This is a favourite in a lower price range https://www.amazon.com/Sleeping-Queens-Card-Game-Cards/dp/B0009XBY3A

Books. My kids love books. Magic tree house is a nice gender neutral option. My son got Narwhal and Jelly last birthday, which is super cute. The LEGO creator sets make three models and have a ton under $15 https://www.amazon.com/LEGO-Creator-Dinosaurs-31058-Dinosaur/dp/B01KJEOCDW/ref=sr_1_5?s=toys-and-games&ie=UTF8&qid=1519156282&sr=1-5&keywords=lego+creator

Science kits. https://www.amazon.com/Scientific-Explorer-First-Blowing-Science/dp/B000BURAP2/ref=sr_1_4?ie=UTF8&qid=1519156359&sr=8-4&keywords=kids+science+kits This one is $15 but I know for sure AC Moore often sells the same one, and bunch by the same company for $10. Plus they often do $9 sales on their large craft kids AND BOGO on Melissa and Doug.

Five Below sells Crayola, Melissa and Doug, Play Doh and a wide variety of board games and other extremely decent craft kits and sometimes LEGO or Megabloks toys.

One last one that has been popular with friends is a small licensed LEGO and matching book. Also runs around $15.

http://www.amazon.com/Lego-Star-Wars-Exclusive-Minifigure/dp/B00JIK7Z7O

lmgtfy

A quick search brought a few things from Brick Warriors. Another route would be to use things from Chima or Ninjago minifigures. Also, Series 5 Dino Man.

I'm gonna need a link to that storm trooper.

Edit: Found it!

http://www.amazon.com/LEGO-9002137-Storm-Trooper-Mini-Figure/dp/B004F12Y54/ref=sr_1_8?ie=UTF8&qid=1418678218&sr=8-8&keywords=lego+stormtrooper

Time to invest

Amazon --- lego zombie. 15$


http://www.amazon.com/LEGO-8683-Minifigures-1-Zombie/dp/B003NYS0RU

Got a link for us Canadians, eh?

Edit: Found it in case anybody else wants it too

My Electrical Engineering department spent over a $1,000 on these https://www.amazon.com/LEGO-MINDSTORMS-31313-Educational-Programming/dp/B00CWER3XY/ref=sr_1_23?hvadid=4967825048&hvbmt=be&hvdev=c&hvqmt=e&keywords=lego+electronics&qid=1575133987&sr=8-23

If you want to be super-hero aunt or uncle, pick up a Lego Mindstorms kit to go with it.

There is.
You can get it here.

These are actually real as well. Expensive as hell though

http://www.amazon.com/LEGO-8683-Minifigures-Series-Zombie/dp/B003NYS0RU

That box in itself is about 900 points, and full of crisis suits and drones. Its actually a killer deal too. I could honestly recommend it to anyone that plays tau. Here it is on amazon. The box msrp is $170, but even at 200 its a steal. Its over $300 worth of stuff, and crisis suits are alot of fun imo.

https://www.amazon.com/gp/offer-listing/B07TT866WY/ref=dp_olp_new_mbc?ie=UTF8&condition=new

I feel ya with those battle plates. I only ever found two in stores..

As for the battle pack, it’s actually still fairly cheap on Amazon. It’s selling for $80

I want to second the lego robotics

https://www.amazon.com/Genetic-Los-Angeles-6029291-Mindstorms/dp/B00CWER3XY/ref=sr_1_1?ie=UTF8&qid=1467523827&sr=8-1&keywords=lego+mindstorms

And legos in general. But definitely some form of programable motion, which lego robots provides

Greed, because it's so beautiful!

Lego Star Wars Exclusive Minifigure: Darth Revan 5002123 https://www.amazon.com/dp/B00JIK7Z7O/ref=cm_sw_r_cp_awd_EOkGwbABRRMJ3

It was a polybag in 2014. I bought one unopened a few months ago. 5/7, so worth it.

MS Spike 01 Builders Parts set comes with flat-top spikes.

https://www.amazon.com/dp/B00MHUQ6X6/ref=wl_it_dp_o_pd_S_ttl?_encoding=UTF8&colid=3M7BFGCM3PD2L&coliid=I29ZIQ5GXBWW88

T'au Vanguard Detachment is on Amazon for $220.

Warhammer 40K: Tau Empire Vanguard Detachment https://www.amazon.com/dp/B07TT866WY

Lot of other detachment kits lists also, but a quick skim through I didn't see Primaris only what looked like regular Space Marines.

This!

You're in luck!

Heres mine
http://imgur.com/WktIvue
And a link (10 dollars = £5.95 according to Google

I love boba fett too<3 so I found you some things you might like.

-these earrings

-this robe or this one

-a little boba

I would like this random Lego person.

You are beautiful!

Here ya go!

Here you go http://www.amazon.com/LEGO-9002137-Storm-Trooper-Mini-Figure/dp/B004F12Y54/ref=sr_1_8?ie=UTF8&qid=1418678218&sr=8-8&keywords=lego+stormtrooper About controller, it's Halo special edition one.

You can't go wrong with minifigs!!

There are various builder parts sets from bandai and kotobukiya such as this you could use

https://www.amazon.com/Bandai-Hobby-Builders-Action-Figure-x/dp/B0087D8K8Q

https://www.amazon.com/Japan-Kotobukiya-Modeling-Support-stapler/dp/B00MG7QWCA

https://www.amazon.com/dp/B0787LX7J8

Also electabuzz vs greninja

https://www.amazon.com/Mega-Construx-Pokemon-Greninja-Electabuzz/dp/B07NMGLBCL/ref=mp_s_a_1_11?keywords=pokemon+mega+construx+vs&qid=1558644218&s=gateway&sr=8-11

It's an alarm clock

https://www.amazon.com/dp/B004F12Y54/ref=pd_lpo_sbs_dp_ss_1?pf_rd_p=1944687562&pf_rd_s=lpo-top-stripe-1&pf_rd_t=201&pf_rd_i=B003M2C0Z6&pf_rd_m=ATVPDKIKX0DER&pf_rd_r=Z8K6KQC3QNGH5WJC018B

I just took the link from the top of amazon.. Not sure if that's how I'm supposed to do if, but here: http://www.amazon.com/gp/aw/d/B005KDIOAK/ref=aw_ls_3_9?colid=386ZUWYQF6KRH&coliid=I9AJY9ZMHWB7L&vs=1

We LOVE Legos at our house!

The 3yo girl we are currently fostering calls spongebob: sponge Bob the pants. I don't correct it, I think it's pretty cute. We don't watch it at our house, but she must have seen it somewhere.

Buy a cheap, moderate LEGO kit.

If you can competently follow directions and put that together, you are MORE than qualified to put a PC together yourself these days.

so cool she is on ice

congrats on the new place!! this would be the cheapest

I saw someone else in the comments mention Lego Mindstorm; that would be a great idea for your son! Not only is the Lego Mindstorm kit still being produced and supported, but there's an entire professional organization centered around challenging kids to learn to build robots: FIRST Robotics

I'm a recent high school graduate and spent four years on a high school FIRST team. I can't say enough great things about FIRST; they're a really cool program that has competitions for all ages where kids get to build a robot to do certain tasks and then compete against other robots.

The very youngest level is FIRST Lego League Junior. While your son might be just a little bit young for it for now, you could certainly reach out to see if there are teams in your area, and if your son is still interested in robots in a year or two, this would be an awesome way to give him another resource to learn and play with robots.

Here's their website, you can read more about it and sign up to get further information here: https://www.firstinspires.org/robotics/flljr

You can also purchase the Lego mindstorm kits on their own, you might need to help him with it and keep him away from some of the smaller pieces, but he'll certainly enjoy watching it move around for now and you can use it to start teaching him how to program with their software. There's a lot you can do with the parts that come with it to get it to drive around, pick up things, etc.

I helped run a summer camp last year centered around Lego mindstorm, and we taught our kids how to make robots that could follow a line of tape using the color sensor, or find their way out of a maze using a touch sensor!

Here's the starter kit: https://www.amazon.com/LEGO-MINDSTORMS-31313-Educational-Programming/dp/B00CWER3XY/ref=asc_df_B00CWER3XY/?tag=hyprod-20&linkCode=df0&hvadid=241989243824&hvpos=1o2&hvnetw=g&hvrand=6335113284905928228&hvpone=&hvptwo=&hvqmt=&hvdev=m&hvdvcmdl=&hvlocint=&hvlocphy=9017517&hvtargid=pla-381559943747&psc=1

And here's their website with the download for the software, as well as some how-to videos to help learn how to program the robot: https://www.lego.com/en-us/mindstorms/learn-to-program

You will need a device that can run the software and write programs, probably a computer or laptop of some sort.

Tell your son he's super cool for already having such a strong interest in robots, I hope he keeps that passion as he grows up! Props to you for looking for ways to support his interests and help him learn more too, that's some A+ parenting right there.

Feel free to PM me if you have any other questions about FIRST or Lego Mindstorm, I'm a huge geek for this stuff and I'd love to help out someone who's also looking to get into it for the first time :P

https://www.amazon.com/Mega-Construx-Exclusive-Spartan-Tribute/dp/B00MHUQ6X6/ref=lp_13245976011_1_1?s=videogames&ie=UTF8&qid=1567687770&sr=1-1

Would be fun to see this work somehow. Whether these are actually a good size or not who can say, they look fairly close though. Is it ideal? probably not. But hey if all else fails. :p

Here you go.

https://www.amazon.com/Mega-Construx-Pokemon-Greninja-Electabuzz/dp/B07NMGLBCL

https://www.amazon.com/Warhammer-40K-Empire-Vanguard-Detachment/dp/B07TT866WY/ref=sr_1_4?keywords=tau+battleforce&qid=1573090512&sr=8-4

if u can afford. its the cheesebox

You had me at Voltron https://www.amazon.com/dp/B07C39J17S/ref=cm_sw_r_cp_apa_i_XUuzCbJN4KH42

Check this out

Same price on Amazon with Prime shipping https://www.amazon.com/dp/B0787LX7J8/ref=cm_sw_r_cp_api_-R4PBb82GWWNQ

Great idea!

*Hops on Amazon*

THIRTY DOLLARS?!

Look at the Amazon Listing :)

Better Trump mini figure