The Day I Lost My Superpowers by Michael Escoffier
This isn't the first or last book where a child delightedly discovers her own superpowers. But it may be just about the driest, funniest, and sweetest, where the discovery is handled with humor, charm, and whimsical illustrations by Kris Di Giacomo.
One of the book's true pleasures is that it's a girl who discovers her own extraordinary abilities, and when her powers fail, as they must, she discovers them in her mom. All of which leads to a lovely intimacy between the two.