Children's books need action, action, action.
You know how "everyone" says you should be able to describe your book in one or two sentences?
I'd go a step further and say that you should also be able to describe what your book is about in terms of ACTION.
"This book is about a girl who ______."
The blank should contain action.
"This book is about a girl who DOES SOMETHING."
"This book is about a girl who grows/wishes/longs for/hopes/realizes/decides to, etc."
Sure - the girl can (and should) grow/wish/long for/hope/realize and decide.
But she should also DO something active while she's growing, wishing, longing for, hoping, realizing and deciding. (In fact, it's the doing that should lead to the growing.)
This book is about a girl who steals a dog in order to make money so her family can get a place to live.
book is about a girl who struggles with her conscience when
circumstances drive her to make a wrong decision for all the right
The first example is the action of the story.
The second example is the underlying theme of the story.
Both are important elements for children's books.
But the character must do something (usually to solve a problem) - and along the way, she can grow, long for, hope, decide, yada yada yada.
So don't forget.