I myself watch cartoons like Adventure Time, all types of anime, and sometimes Family Guy or American Dad.
Younger children shouldn't even by watching any anime or Family Guy and American Dad because anime has a ton of violence most of the time and obviously Family Guy and American Dad are for adults and teens.
I don't think cartoons are bad most of the time. Yeah, there's really violent and stupid shows. But kids shouldn't be watching violent cartoons and anime anyway.
People that take what happens in cartoons or anime seriously and do it in real life are just, pardon me for saying this, plain downright stupid.
I watch a show called Doctor Who where the main character fights bad guys and aliens. Do I go out looking for bad people and start beating them to a pulp or blowing them up? Nope.
The people that did that to the little boy were messed up in the head to even do that.
They would have done something else just as bad without cartoons, because, like I said, they were messed up in the head. No one in their right mind would kill a little boy.
And is your nephew a younger child? Because children don't know things are wrong or annoying, they're young and inexperienced in this great big world. I suggest being patient with your nephew and just playing along. c: