I had kids come to my house first, so I could see how they interacted with my children. Some of them were too immature and young to sleep over (and I had to bring one child back who missed his mommy). The age of first sleepover was about 7-8, depending on the child. Once I knew for certain that the child was pleasant and came from a reliably kosher home, and had met the parents, I started with playdates at their home, and eventually, sleepovers. Most of my kids loved going away, most of their friends LOVED coming to us for a Shabbos (maybe I made better desserts). I loved having the kids’ friends over, and still do.