Reddit reviews Fraidyzoo

Not Afraid of Dogs might be very relevant, about a boy who overcomes his fear of dogs when he discovers a visiting dog is afraid of thunderstorms.

Little Dog Lost is a sweet book based on a true story of a dog's rescue at sea, with a very happy ending!

Good Dog, Carl is an almost wordless story told in beautiful illustrations about a dog left in charge of the baby while the mom goes out, and all the mischief they get into together. The dog is a big rottweiler, so the depictions of his gentle interaction with the baby might be especially helpful. There are also a bunch of sequels (Carl Goes Shopping, Carl's Birthday, etc).

Officer Buckle and Gloria is a hilarious story about a police officer whose safety talks are made entertaining by the silly antics of his police dog (not portrayed as scary at all).

Martha Speaks is a classic, about a talking dog who saves the day (if rather unrealistically!). I believe there have been a few sequels written as well.

Excellent Ed is another very silly story about a dog trying to figure out what he does best.

In terms of early readers, the Biscuit series features the adventures of a cute puppy, and there are TONS of them. Henry and Mudge also features a dog, at a slightly higher reading level.

If you're looking for true stories told in photos, Tuesday Tucks Me In is told from the perspective of a service dog to an Iraq veteran, and Tarra and Bella is a true story about a dog who befriends a lonely elephant.

May I Pet Your Dog is a great book that teaches kids how to safely meet a new dog (holding out your hand to sniff, etc). Probably not the best to start with, since it does mention unfriendly dogs and what to do if you encounter them, but once you work up to meeting some dogs this might be helpful.

Lastly, though it's not about dogs specifically, Fraidy Zoo is a fun book about a girl who is afraid of the animals at the zoo and how her family creatively helps her overcome her fears!