It's not particularly clear to me what level of mathematics you're aiming for, but for example I found [1] & [2] interesting when I was a young teen, and lettin

It's not particularly clear to me what level of mathematics you're aiming for, but for example I found [1] & [2] interesting when I was a young teen, and letting kids explore of the series of books by the MAA [3] and AMS [4] would certainly spark their interest. In short your best bet is to get them to a library, and let their interests take them where they want to go. [1] http://www.mathmosaic.com http://www.mathmosaic.com [2] http://maa-store.hostedbywebstore.com/INGENUITY-IN-MATHEMATICS-Ross/dp/0883856239 http://maa-store.hostedbywebstore.com/INGENUITY-IN-MATHEMATI... [3] http://maa-store.hostedbywebstore.com/Popular-and-Expository-Books/b/3232536011 http://maa-store.hostedbywebstore.com/Popular-and-Expository... [4] http://www.ams.org/bookstore/mawrldseries http://www.ams.org/bookstore/mawrldseries