I don't know much about developing math talent. The advice I read was to train a kid to a middle school level then hire a private tutor from a University. I don't know if that's what will happen. I do want to stock my house with books for the kids to grow into. My limited library includes:
The Disappearing Spoon
by Sam Kean
The Wizard of Quarks
Alice in Quantumland
Scrooge's Cryptic Carol
by Robert Gilmore
George's Cosmic Treasure Hunt
by Lucy and Steven Hawking
Any other can't miss classics?
I've seen the name if Ma Lipping "Developing Math Talent" mentioned.