Anonymous wrote:I think it’s fine if girl is 9.
I agree. Our best family friends have 14, 12, and 9 yo girls and an 8 yo boy. I have 12 and 10 yo girls and a 4 yo boy. Usually both sets of parents are present too, because we live a few hours away from each other, but there have been times they've slept over together. I agree the dynamic might feel different if the sexes were reversed. But I don't think it's much different than allowing your daughter to sleepover at a girl friend's house who also has a brother.