I think it really depends on the child and the situation they have been placed in. I think now days kids are seeing more and more of that on tv and other places. For me I would say that its not normal or atleast I wouldnt want my 5 yeat old to be asking me about sex. I think its really just a call as a parent as to wether or not you think its normal. If you havent been exposing them to that kind of stuff they have to be hearing it somewhere. I think 5 years old is a little to young to be asking about sex.