How did you explain the Boston Bombing to friends/Children?

I just simplify it and speak frankly. My younger kids are now 10 and 12 so more able to handle it but if they were younger, I'd tell them that there were people who wanted to hurt other people and they set off bombs at that race. Some people died and many were injured. We never know where something like this will happen but it's not common for people to be injured in their every day lives and we trust God to do what is right. While He doesn't purpose these things to happen, He is still in control and allows this for whatever reason that we may not know until we get to heaven. What is most important is to know that the children are loved, we will protect them to the best of our ability and the rest is up to God. Then hug them.