I don't know what it is but my kids love sleepovers with each other. I only allow them on Friday nights since Justin has school but they ask me all week long when is Friday mom. They look forward to it. I love how they set up their little beds and put their stuffed animals in their own little houses and blankets too. It is really fun for them and a fun way for there relationship to grow. Occasionally we give it a try with Megan too but she seems to have a harder time still. Maybe when she's a little older I guess. They don't always go to sleep right at 8 o clock bedtime but usually within a few hours this is how they look. Ah peace and quiet.