From the title of this i thought the thread may have been about kids having sleep overs at other kids houses, which is a debate for us at the moment. I have told dd she needs to wait till she is 8 for that.
But her first sleep over was at my mums when she was 3 months old - we had a wedding to go to (and i had such a horrible night, its terrible fretting over the first time you leave your baby!! i still remember that awful feeling in my gut)