Traumatic world events are difficult to contextualize for children this young. It's not on the same scale as an event that touches them personally, but makes no impact on any larger scale (say, a pet dying or a parent or sibling being injured). Their knowledge and lasting impact depends entirely on their parents, who are their emotional models.
Never once in my life did I think I would hear an actual explosion, nor did I expect to be in walking distance of a terrorist attack. No one ever plans for these things, nor are you ever really prepared. My experience in Paris reshaped the way I look at studying abroad. In no way will it stop me from traveling, but it will make go about it in a different way.
Right now, I'm going to let my tears fall in the shower, instead of in front of my child. I'm going to turn off the television, close the Facebook tab, toss the paper in the recycling under bottles and cans. I'm going to let my daughter play and laugh, and not know all of the terrible things that I have to know.