I think it's an important part of school. Sadly, it happens all too often. I'll never forget the day that the grade 2 class I was in was doing doing a unit on sexual abuse and right and wrong touching. I felt a feather-light tap on my knee and one of the little girls leaned over and whispered very softly "that happened to me, you know". Thankfully, the teacher had told me about her history in advance, but it still broke my heart. This precious child was in foster care as a result of the sexual abuse and of physical abuse that left her with permanent brain damage.
It's important to give children the proper language, too. I remember one example that was shared with us in one of my sociology classes. One of the kindergarten students told his teacher that grandpa kept playing with his toy. This went on for several weeks, because the teachers realized that there might be something more to it and investigated further and realized the boy was being sexually molested by his grandpa. He'd been trying to reach out for several weeks but didn't have the right vocabulary so the abuse continued.
Kindergarten is not too young to begin talking about right and wrong touching. Many resources out there are able to put it in a very gentle and unfrightening way.