I really think it depends on the child. For me, animal cruelty and violence against children, particularly sexual crimes, are always most personally disturbing.
To this day, I try to avoid these types of stories, as I become personally fixated on the victim's suffering and have difficulty getting over my sadness/vengefulness on their behalf. I generally read The Economist, The Atlanic, and Ars Technica on an ipad, and these give me the "hits" I'm seeking-- economics, politics, technology, and current issues, so our household is fairly benign.
I store up my wrath over the world's many injustices and pour it into raising my son to be a good person, as well as lobbying my elected representatives and working in the non-profit sector. I know that my efforts contribute to protecting the vulnerable, and that's the message I want my son to hear when he's older: you must rise up against oppression and demand change. I want his first exposure to weighty issues to be through seeing my husband and I working to overcome the challenge, because I think an internal locus of control is necessary for not becoming overwhelmed by the senseless violence and injustice in the world. So my answer is that he'll volunteer alongside us from an early age and meet real people impacted, from the perspective of being the solution. It's a little Harry Potter-esque, I guess.
Not sure if that is helpful, but that's the untested approach I'm thinking I'll take.
