College grads are a "better bet" in terms of the probability that they'll succeed, but not in terms of additional investment making a difference. Spend time or money on/with a recent college grad who's already primed to succeed, and neither you nor society will get much that you wouldn't have already. Spend that same time or money on/with a child whose mind is still malleable and whose future is still uncertain . . now you're talking about a real possibility of making a difference.

Any random baby, maybe. Also there's the issue of malleability.