A few ideas for nurturing math -
1.
Roman Numerals, which is NOT part of Common Core, and therefore is no longer taught in some schools.
2. Math and Logic Puzzles.
-
The Moscow Puzzles- related books which may be of interest are listed on the Amazon sales page.
3. Cartoon Guides to math, including
Algebra,
Statistics,
Calculus, Economics (
Micro,
Macro)
4.
Life of Fred math sequence, plus
Financial Choices.
5.
Middle School & High School Math Talent Search. Although too young to compete, you could gather the problem sets and solutions to past problem sets, for him to practice with for possible competition in future years.