Personally l do think its too young, 90% of abuse is by someone a child knows....why take the risk, they have their whole lives ahead of them to stay at others homes? We always think it could never happen to OUR child in THAT persons house but it does.....
Also there is the more minor risk of unsupervised internet access etc.
I think its worth waiting until the child is old enough to know what to do in a situation they were uncomfortable in, and get themselves out of there...
My DD has started having very limited sleepovers now but she is almost 12 and quite capable of assesing a situation, knows how to call a cab and get home in an emergency if she couldn't get hold of me or her father immediately.
When l was a child l was allowed to stay at a schoolfriends house, my parents had known them all their lives, they lived in a neighbouring village..
.her father was a pervert who secretly abused her for years and l often had to dodge him...luckily l always managed to, BUT l had no idea of the danger l was in, thought he was just v odd.
I never told my parents, as a very naive 10 year old l would not have had the words to explain why exactly he was odd, and would have been embarrassed to say his trousers were often undone....
I have since told my now elderly parents and they are truly horrified, they still see my friend and she has gone public with the abuse...
Please, please don't risk it, unsafe men are everywhere in society and often it stays secret for many years.