I feel like @truthtellah has the most reasonable answer so far. I'm not asking about violence in video games; that's not the point I'm getting at. I'm asking why is violence against children a taboo. Apparently other than being "politically sensitive", the only reasonable conclusion is that overpowering the powerless seems to be frowned upon.
But meh. Give me a break. As long as one has strength over another, it would always be a "strong overpowering the weak" scenario. This is part of our humanity; embrace it. Don't shun it.