Read, read, read. :) And expose him to lots of different topics. When I was gorwing up my parents made sure my brother and I got exposure to a little bit of everything. We were always at museums and always exlporing or learning something. Not in a dry textbook way but always in a fun "lets try something new" way. We did science experiments at home, read folk tales from other cultures, and when we did watch TV it was PBS and my parents watched Nature and Nova. And that joy of learning and openness has carried over into our academic and then adult life.