Polish your manuscript. Make your manuscript the best possible version of itself.
Do this before you show it to an illustration partner. And definitely do this before an editor or agent reads it.
To polish your manuscript, set it aside for a while. Then you can look at it with fresh eyes.
It never hurts to ask beta readers to give your manuscript a once-over. This is easiest when it’s short, like a picture book or chapter book.
A beta-reader should be someone you trust to speak honestly. Hopefully, your beta readers have experience with children’s books professionally. Maybe they’re a librarian or teacher?
Finally: read your script out loud to kids. Watch their reactions. When do they laugh? Do they get bored?
If they’re old enough to respond, ask them for feedback. Brace yourself: kids are honest!
With feedback in hand, revise. Then, revise again! Polishing takes time and multiple drafts.