What role does the theme of the story play in children’s book?

The theme is an important aspect of writing children’s stories. This is what builds the story and makes it worthy of being read. For a child, it is the lessons which are showcased by the inspiring characters of the story, making it memorable for the children. On the other hand, they are not very clear or comprehendible for the children. This is where cheap illustrator for children's books make use of amazing illustrations to make the lessons more legible through the description of the actions taking place in the story. What do you have to say about it?