How do you explain things to a 6 year old?

So last night....I'm putting my son to bed. I always sit with him for a bit while he relaxes and drifts off. I have no idea where his thoughts come from. I don't like to think that his innocent, little brain is thinking about such serious things. He started talking about death and war and bad guys and such. He asked me why God allows such things. I didn't really know what to say or how to explain it. How do you make sense of it? I don't even know why. Is God trying to teach us something? Are we supposed to learn and grow from the bad things in life? S. told me that when he gets to Heaven, the first thing he's going to ask God is why he lets wars happen, why bad guys exist. I told him that would be a good thing to ask God...that God would explain anything and everything. I've always heard that you're not supposed to question God or His plans. Still...how do you come to terms with the hatred and fighting? I honestly don't know. In my heart, I want world peace. I know that sounds like some beauty pageant statement, but it's true. I don't understand why we all can't get along. Why can't we love each other? Why can't we respect and embrace our differences? That's what I believe God would want. I told S. that I prayed for world peace. That the bad stuff in the world didn't make sense to me and I couldn't really explain it to him. He's 6 years old and these things are in his thoughts, for pete's sake. When I was 6, from what I can remember, I didn't think of such "heavy" things. I remember how life seemed so much easier, so simple and carefree. Of course, I was a child. I didn't see the world through adult eyes. When I was young, it was safe to play outside with your friends. It was safe to ride your bike through the neighborhood. You didn't have to worry that some stranger would kidnap you and hurt you. I sound just like my parents. Their memories of..."I remember when I was young. We'd take the trolley downtown and see a movie for a nickel." I used to think...yeah...right. You obviously lived a zillion years ago. But here I am...doing the same thing. "I remember when...." It just hurts my heart that I have to try to explain such negative things to my son. I have to somehow explain the evils in the world. I have to help him make sense of these things. And it's difficult. I have a hard time with it myself. I wish life was simple. I wish we didn't have to worry about the danger in the world. I really wish we could all get along and live together in peace. Maybe that sounds hokey but I believe that's what God would want. It's what I want. I wish.