​While these were written for children, they are just as true for adults.

1. Do not try to keep what is going on from your kids. These videos on are Snapchat and other social media. Even elementary school kids talk about shootings. Focus on how people came together and helped out to keep people safe. Your family style may be to protect the kids from this reality, but many other families are telling their kids and then all kids talk to each other in school.
2. During the unfolding of a tragic event such as Parkland School Shooting and other situations, most TV is live and you cannot anticipate what your children may see. Turn on the radio or show them pre-recorded news broadcast.
3. Talk to your kids about the event that is happening in simple language that they can understand, which is age appropriate (i.e. Some bad people shot at some people in a building etc. Some people are hurt and some have died)
4. Reassure the kids about their safety. Tell them that while this is important that most of the world is safe and that the area you live in is safe. Also, reassure them that the police, security and many other government officials are doing a lot of things to keep them safe.
5. Children need words. Tell them what you are feeling, what you think about the situation. Then, encourage them to talk about what they think. It is important to validate their feelings and clear up any misunderstanding and misinformation they have.
6. Be proactive and find ways to help. Say a prayer, light a candle, give blood, go to your place of worship, you and your kids can donate some money to an organization that is helping with the situation. Make sure some of it comes from your kids, no matter how small the amount.
7. Reassure your kids a little more, watch them a little more, do obvious gestures that show you are keeping them safe and watching over them. Remember kids may have very illogical fears.
8. Kids grieve very differently from adults. They may not talk about things for weeks or months. Be available to talk about their grief whenever it may come up.
9. Keep as many normal routines going as possible; but, allow a little more time knowing that grief is exhausting for you and your children. Routines are very important, because doing normal things in abnormal times help us to feel normal again.
10. Remember for your kids and for yourself, the concept of possible vs. probable. School shootings are possible anywhere, anytime, but they are not probable in our lives today. But are children should know what to do. While events may be tragic, try to put losses in perspective; that many things we do are risky in life, but we do them because fear does not stop death, fear stops life. Most of us will go to the movies and be very safe.

Source: 
Grief.com
David Kessler