Different gender sleepover

My 5 year old son has a girl in his class that he is very good friends with. He has asked us several times if he can have her over for a sleepover. My wife and I do not see an issue with it being they are so young. They are both great kids and well behaved. I recall when I was younger, even as old as 8 or 9, staying at a friend of mines house who is a girl.

I am just curious if any other parents have done this and is it appropriate to ask the other parents. My wife and I worry it might come across as weird if we bring it up. Any advice on the approach or appropriateness is helpful!