I dated a man who at the end of WWII lived in Germany. American soldiers gave him and his friends candy in exchange for sex. He is still torn apart about it today blaming himself. He was about 7 and there was no other candy to be had. The Americans were friendly to all the kids. Some took advantage.
Power and opportunity made it possible.
I believe the first line of defence today is for parents to openly discuss the issue with their young children and make it absolutely clear that if anyone approaches them inappropriately, they are to leave and come home immediately and TELL MOM and DAD. Children need to know that their parents will believe, support and protect them.