One Montessori mantra that comes to mind is "brief and true". It's the idea that whenever you're speaking to young children between the ages of 3 and 6, you should keep your statements truthful and concise. Children are unlikely to listen to a lecture. Instead, they want you to give them something to help them understand right that minute.
So far Coco hasn't asked about what happened in Paris, but, when she saw the photo of the refugee child who had drowned on the beach in Greece, she was curious. "What happened to that boy?!" she asked. I explained that his family had to leave their home, so they traveled to the sea and tried to go across it in a little boat, but the boat turned over and he died. Pretty brief and all true. This led to Coco asking why they didn't just stay at home. I responded because their city was full of fighting and wasn't safe; they didn't have anywhere to live or work or play, and no table at which to eat their food together.
She thought about it for a minute, then her eyes grew wide and she asked me, "In this world?" Yes, Coco. In this world. I find it hard to believe, too.
Try to avoid over simplifying or phrasing like "bad guys". It's also important to avoid making the issue black and white. Life is messy and grey most of the time. To suggest otherwise would be false. Children appreciate when their intelligence and status as fellow human beings is respected. They're not emotionally or intellectually ready to have the whole story, of course, but they need to hear honest information that they can understand, relate to, and digest.
I genuinely believe that it strengthens our children's capacity for empathy and compassion when they are exposed to some of the harsh realities of life in a way that they can comprehend. So, keep it true and brief rather than keeping them in the dark. What do you think? How do you approach these issues with your children?
Also, a great podcast about talking to kids about death.