I agree with the anon that said it's a trust issue.
But, as I explained to my teens, it's not just a matter of trusting them - it's a matter of not putting them in the situation where they have to control other people's actions. This way, there isn't any case of this friend was invited, then they invited a few people, who invited a few people...
Plus, it's a good idea to check with the other parents to see if they mind. My dd got invited to a sleepover when she was in 8th grade. They had gotten together for sleepovers 1 or 2 times before. I found out that for this one, it was going to be our 2 girls (8th grade at the time) , her 15 yr old, her 15 yr old's friend, and possibly her 12 yr old ds and his friend, while she and her friend ( I think the other boy's mom, not sure) were going to be "out at the casino" and they were going to be home alone until about 1am. I wasn't comfortable with that, and said no.
at 9:36 AM on Sep. 1, 2009