IMO if your child is 18+, working full time and living at home they should be paying some rent. (I think my only exception to that would be if they’re saving money to go back to school). Or if 18 seems unfair let it go until age 21 then if they’re still at home then I would for sure be collecting rent. It’s a good life lesson and once they move out you can always give it back as a gift towards an apartment, home, car etc (if you’re financially able of course). Individual circumstances are all different and that’s just how I see it.