I know with my kids . My daughter I made it at a certain age she could go to them.
But I had to know the parents very well.
I also made sure there was not too many kids there other wise how can they watch them all .
When my daughter had friends sleep over it was only a few at a time.
I knew every one of the parents and had all thier phone #s in case something came up.
I also did not go to sleep till they did.
I remember being young lololol

imo 7 is a little young
imo the 11 year old should be ok
hope this helps
muffy