I've got one who's very into books, and the other is very into audiobooks. Once place where my eldest child was exposed to a lot of simple cryptography and cry

I've got one who's very into books, and the other is very into audiobooks. Once place where my eldest child was exposed to a lot of simple cryptography and cryptanalysis was in the books of Emily Rodda (Deltora Quest). She makes many plot points out of various introductory codes to be cracked.