I cannot believe that some people think it's innapropriate for children of opposite sexes to play in a bedroom together.
My DS1 is 15. If we have my niece (10 and yes, she is physically grown up for her age) round or my neighbours DD, aged 8, they often go upstairs to play on the PS3 for a while. It would never occur to me that a) the girls would be in any danger from my son, who is well aware that no matter how physically developed a young girl may be, 10 and 8 year olds are simply children and he views them as such, little children, or b) that my son would be in any danger of accusations or being 'led on' from these little girls, because they are just that, little girls interested in all the usual things little girls are and that doesn't include anything sexual with boys IMO.
Vile, vile, vile that anyone could think any different and also bizarre that people think any sort of abuse can only occur in bedrooms.