While you are under no obligation to take care of your child or grandchild once they've
reach adulthood, they're still family and you want to help them. But you should set guidelines in advance such as rent, chores, house rules, guests and alcohol/smoking use. Is there a set date for how long they can stay? Are there any consequences for not obeying the rules? Even if they can't afford rent they should still earn their keep. The free ride is over and mom is not a synonym for maid. Also, if your child has a child, you need to establish rules regarding babysitting as well. (Kiplinger offers a great sample contract).