Kindy? Abuse? What to look out for.

I understand your feers, my son was non-verbal when he started preschool.

Something to bear in mind. Kindies are really busy places. Parents coming and going at different times lots of staff coming in and out and very strict guidelines. Plus with majority of kids being independent at toilet training etc generally it isn't an easy obvious target for pedophiles.
For example children aren't allowed to sit on laps or be held/carried by staff.
The incidents that happens recently in SA were where staff were in alone with children eg foster carer who had sole access to children, or many years ago a bus driver who was alone in a bus with children.

The schools/Kindies I've worked in we had an open door policy, so no door was to be closed, most rooms had Windows so were not exactly private etc. if we did need to toilet a child for some reason (we all knew which children they were) we were to stand at the doorway, not in the cubicle etc.

I would discuss the conversation/question and teaching protective behaviours with your sons speech therapist. As they know your son best, there might need to be some ground work done so your son can understand certain questions etc.

I just want to reassure you though, although it does happen and it's awful when it does, it doesn't happen very often. It's very rare, but of course when it does happen, it sticks in our minds. So it's important to be watchful but not be fearful, if that makes sense.