My nephew is 9 and very frightened by all of this. He's actually my cousin's son (her folks raised us when my Mom died, so she's like my sister & I call her that). Last night returning from a prayer service in their small town, he was very silent until he finally asked his Mom how many things like this his Grandma had lived through. She thought a minute and said: "Well, she's 87, and lived through WW1, the Great Depression, WW2, the Korean War, the Cuban Missile Crisis, President Kennedy's assasination, the Vietnan War, Chernoyl nuclear disaster, the Gulf War, and now this."
That seemed to comfort Leland, to know that people can live through disasters and wars and still believe in God and that there is goodness in the world.
Remember, we can overcome this too. Let your children know that they are loved, hug them tight and make them feel safe. This may shake our feelings of security and safety and trust, but children need to feel their world is still safe.
I pray for all of the the victims and their families, may God hold them close to his heart and comfort them.