The first thing you should do is talk to your child. Find out exactly what it was she saw, and ask her why it upset her. Then reassure her that you, your partner, her teachers, and plenty of other adults in her life are doing everything possible to make sure that she stays safe and unharmed.
You may find that it’s an incidence of violence that has upset your child. It’s important to reinforce the idea that this kind of violence is not normal, or acceptable. Let your child role play with you if talking about it is difficult. Give her a chance to scare you during play, to help her cope with the emotions she is feeling.
If you have fears of your own, it’s also important that you work them out too – speak to your partner, a church leader or a professional to work through your fears, so that you can avoid passing them along to your children.
Another wise idea, particularly with very young children, who may not understand violence yet, is to limit their watching of television around the time that the news is on. They don’t need to know all about the bad things that happen in the world yet, and since it is likely to be upsetting, it’s best to simply avoid the issue for now.