Last year I flew my father and his wife Biz (on DL so no first) from BRU to MDT. They came for 10 days to watch our kids while DH and I went on a 10th anniversary trip to Jamaica (we were only gone for 6 nights, but flew them in early to settle in) This was one of the best uses of our miles.
I have also done the same for my Mom when she has flown out to visit us and watch the kids. I am immensely grateful to have the miles to do this as it really makes for a win-win situation.