There are too many to list.
An idea for finding profitable passtimes: look at all the intricacies of how some profitable business is run. Oops, you just found a bunch of profitable hobbies, but how do you like them?
>can easily pay for their college, but self-sufficiency
The purpose of childhood (remember that the human organism, including the brain, is only fully developed @~30y), is to become the best adult. The best way to become the best adult is to focus all effort on the most effective way to become the best adult. Worrying about how to pay for college and spending time trying to pay for college are not effective ways to become the best adult. There are better ways to have one become self-sufficient, such as having them know the benefits of being self-sufficient (if that's not enough, they might need help understanding the idea of self-interest). If you, as you say, have sufficient funds to pay their tuition, why not loan them, at market rate interest, for the tuition. If you trust them, you might do it informally, but if you need, you can have professionals draft the contracts. Or is your money busy?