Reddit reviews Sex, Gender, and Sexuality: The New Basics

Here is a book that is free on Kindle (App for phone or computer also be free if you don't have a kindle).

Here is a book that is just what you said you are looking for.

This book is a little more sociological but cheaper than the one above

I love this website on Gender and Sexuality

Here are a couple of lists of good books around trans issues for kids/teens:

https://www.roomofonesown.com/trans-teens

https://www.huffpost.com/entry/the-21-best-transgender-b_b_9702762

https://www.bookish.com/articles/21-must-read-books-for-transgender-awareness-month/