How and when should a child be introduced to Buddhism?

My son will be four soon. I would like to introduce him to Buddhist philosophy, and some meditation practices. However, stillness is, at this point, completely foreign to his personality :) My wife is Christian, and has taken him to church a few times, but not regularly, or recently. She and I are okay with sharing our differing beliefs with our son. I'm not active (or aware of, really) any local Buddhist groups, and, unfortunately don't even meditate regularly anymore. Still, I think meditation, and an understanding of the philosophies, would be very helpful to my son, and I'd like to get him involved as soon as is practical. How do I best introduce him, both to meditation and Buddhist philosophy? At what age is he likely be ready for either?