Sleepovers are an easily avoided highly risky situation for children
I work with children who have experienced sexual abuse. Most of the time the perpetrator is a member of the child's own family, but I've also worked with DC who have been abused by teachers, youth workers, members of their church, neighbours, occasionally complete strangers.
I was also abused myself as a child and the abuse always happened during daylight hours, while one or both of my parents were in the same building, the perpetrator was someone they knew well and had no reason not to trust. So as a survivor of CSA, when I inevitably get anxious about my DC having new experiences and interacting with people outside of our family and close friends I remind myself that it's ok to be anxious, but cannot let my anxiety stop my DC from experiencing a normal childhood. Unless I keep them with me 24/7 and never let them interact with anyone at all, there will always be an element of risk. But risk is part of life and a big part of my recovery has been accepting that.
If a sleepover is too risky then what about playdates at friends houses, will your DC be allowed those? Or do most people think paedophiles only abuse DC after dark?
Also this idea that it's unsafe because "you don't know them well" is curious to me. Do you think that if you got to know them well you would somehow be able to suss out whether or not they're sexually attracted to children? Paedophiles aren't all weirdo loners. We might like to think so because the reality, which is that most of them have families, friends, people who love them and trust them, is not a comfortable one. We like to tell ourselves that people we 'know' couldn't possibly pose a risk to our DC but honestly we have no idea.