This might be controversial, but I'm just not a fan of sleepovers. Part of this is my own history, because one time, I was staying over at my best friend's house at the same time that her older brother had a bunch of friends over. They were probably around 10 years old. I thought I'd slept soundly through the night, but the next morning, they all thought it was HILARIOUS that I had gone sleepwalking. I remember feeling really weird and vulnerable about having no memory of that.
These days, my hesitation around sleepovers goes beyond my own childhood embarrassment. As a parent, it comes down to this: You can know someone well and still not really know them. You just don't always know who people are in their home. You don't know how parents talk to each other, how they handle conflict, who else has access to the home… the list goes on. A family can seem lovely from the outside, and most are. But the risk of getting it wrong isn't one I'm willing to take.