Introduction to Modern Cryptography by Katz and Lindell is from a pedagogical perspective one of the best-structured textbooks I've ever read on computer science topics (and in general, but my exposure to textbooks is a biased sample). It goes into the foundations of cryptographic theory and gives a good basis for understanding and contextualizing even advances that have been made since its publication. I think most children can grasp difficult material if an adult that's good at the meta-skill of teaching is helping them with it via individual attention

Thanks for the recommendation.

"I think most children can grasp difficult material if an adult that's good at the meta-skill of teaching is helping them with it via individual attention" That's how we feel too and they appreciate being given that chance if we don't push.