Are the KDP keywords right for a children's book?

Yes. When the book's first and last levels are both children's levels (Very easy to Medium), the keywords are for kids (for example "maze activity book for kids ages 4-6", "easy mazes for preschool", "puzzle books for kids gift"); otherwise they are for adults, with "hard mazes for adults challenge" when the book reaches Expert or Extreme, and "large print mazes for seniors" in large print. They change by themselves when you change the book.