I have two friends -- both grandmothers. One has a number of health issues, including migraines which seem to be aggravated by stress. Her two sons and DILs are constantly dumping off their kids for Grandma to babysit. My friend loves her grandkids -- don't get me wrong -- but the stress of caring for overactive toddlers and pre-schoolers is killing her. Yet she will not talk to her sons and their spouses about the situation.
My other friend, however, told her kids right from the start that, while she loved them and their kids, do not expect Grandma to be their default babysitter. Grandma will babysit if there is really no other alternative, but the kids should either take their children with them, stay home or pay someone to watch the kids. In my friend's view, she raised five children with no help from her ex-husband or anyone else. Now it's time for these children to raise their own kids.