For my children, as long as they are in college, they can stay home and not pay rent. But they have to put the money towards the college tuition so they are not in student loan debt when they get out on their own. However, if I saw my child was not being responsible with the money, I would charge rent ($100/mo or so). If you don't need the money, put that money into a savings account for them (without them knowing) and give it to them later when you see that they are more financially responsible.

If the child did not go to college, I would definitely charge rent, more than $100 too!

I think it is so important for people to learn financial responsibility before they move out on their own. I've seen too many people fall flat on their faces when they move out and get into so much debt they can't get out. They need to learn early that they will have lots of bills and they can't spend all their money on frivolous items.