My experience has been, like others, that parents generally drop their kid off if it's at somebody's house, and stay if it's at a public place. Because it's just harder for the hostess to keep an eye on the set of 8 kids among the other two dozen at a party place or roller rink, than it is to keep track of 8 kids who are in her home. Maybe once the kids are older elementary/middle and can pretty much be responsible for themselves, but usually before that, parents stay. At a house, parents usually consider drop-off around 5 or 6, depending on the kid. At my daughter's 6th birthday party, all of the parents asked me if I minded if they left. I didn't, so they did. The one exception was a friend of mine, and I think she stayed to keep me company (and to serve as a second pair of hands, which I appreciated) more than because there was any sort of social obligation. When my two older daughters (6 and 4) were invited to a party for a 5-year-old, the mom told me I was welcome to leave or stay. The party was a good half hour from my house, though, so I didn't see the point in driving home, and my kids wanted me to stay, so I did. Lots of parents were there and I had some good conversations.