Vocabulary is a good question when writing for children.
I asked a friend on writing.com about the word. She has a children's book published which is why I figured she would know the answer. And the verdict was; okay. It is a good idea to put in a couple of new words for children, especially if it might be a story that is read aloud. Just don't go overboard with the difficult words.
Today I am writing Hazel & Lilly. It's a story about a girl and her new imaginary friend.