First: It can't be overstated, like on an airplane that loses pressure...PUT ON YOUR OXYGEN MASK first.. Whatever that looks like for you... whatever helps you to mindfully care for you, do it FIRST. Your mindful moment may look different but some basic ideas could include more time in prayer, meditation, listening to music, essentially doing whatever it takes to GROUND YOU!
Second: Accept this is bigger than all of us. No one has THE right thing to say...
Third: Be there for the children in your life with honesty and transparency. As you likely already know, kids are sensitivity magnets so while you don't want to add to the burden; pretending that life is business as usual right now just won't fly. Consider ways you can support them in processing their feelings without trying to solve what can't be changed.
Fourth: If they can, help them reflect on something they are looking forward to in the future.
Fifth: Tell them they matter and you are proud of their strength.
Sixth: Back to putting on your oxygen mask first...Breathe, take deep breaths throughout the day (even if it's 5 extra visits to the bathroom, just to have your own mindful moments).
Seventh: Repeat steps 1-6 as often as you need to.