Raising them to share "rationalist thought" seems hard. Nearly everything I can think of seems to have a real risk of ending up being either password guessing or raising an overly enthusiastic contrarian.

The single most important lesson of rationality that I think a child can grasp intuitively through experience seems to be "beliefs should pay rent". But constructing lessons, engineering situations, setting an appropriate example and most importantly finding a peer network to reinforce this, appears to be... a difficult undertaking.