I have only seen the Press characterizations of what happened.
I don’t know if the kids were exposing themselves to each other playing doctor, or if the boy was forcibly raping terrified toddlers. I tend to think that it was more like the former.
If there were horrifying details, I believe that they would be gleefully revealed by the media. Nowadays, the term “Sexual abuse” has been stretched to cover things like poor choice of words.
True, that. If your kindergartener gives another kindergartener of the opposite sex a hug they don't want (eeeew! cooties!) in some jurisdictions they can be written up for "sexual abuse".
Without knowing the details, it is hard to say what is appropriate.