Well, being a parent of a small child (smaller in her class) I worry about my child's safety all the time. I would say that certain decisions that parents make are because they are parents, and think differently about the situation than a person without children would.
If my daughter was in an organization and their was a child (any child, but we'll say that they are mentally handicapped) that showed signs that they could be harmful to her, I would first find out if other people agree (which is the beauty of how most organizations work) and if they do, find a way to dismiss the child. If they didn't agree, I would remove my child for their safety. We shouldn't have to make all decisions on whether or not it is politically correct. We also don't have to make a group suffer so that one person is not left out.
And, if my child was the disabled one, I would also worry about my child's safety and the way the child would be treated.
When I was in highschool, I volunteered to help in the disabled class. I was kicked, hit, slapped, and had things thrown at me by mentally disabled children that could not function in a normal capacity. It's easy to say that every child should be able to participate in activities, but in reality, there are children that endanger others, and as adults we need to decide what is best to protect our children.
Myrrander, you're starting to sound like a liberal nut case again
I don't think that the parents don't want their children exposed to "other" people, they are just concerned over their child's safety. If all parents were as concerned, and forced other adults to do the same, this world would be a safer place for our children. Instead, it's an adult world where it is OK to swear on radio and TV, kids see images on prime time that they shouldn't, and adults want equal opportunity for everyone even at the expense of a great number. Political correctness is great, but it's not always reasonable or best for the situation.