First of all, my heart goes out to those affected and their families. As a father, I can't begin to fathom what they are going through right now. I keep thinking about what I would do if something like this were to happen at my kids' school and I'm having a hard time wrapping my head around even that.... My prayers are for God's grace to be with those affected.
I think it's too soon to get into the causes, the why's, or the politics involved in what has happened today. I have my own (very strong) opinions as I imagine we all do. Now is not the time to get into gun control, mental health issues, our morally bankrupt society, or (heaven forbid) conspiracy theories.
I would like to touch a few thoughts about things we might be able to do to protect our families in a "active shooter" scenario.
First of all, you need to have an action plan for escape and your entire family needs to understand it. If at all possible, you need to get you and your family OUT as soon as possible. Develop a plan and draw a mental map of escape routes every time you enter a potential target for an active shooter.
I know it might sound a little paranoid, but movie theaters, malls, and schools are places we frequent and should be safe. Should be. The reality of the world we live in is that this isn't the case anymore. Pretty much any place where there is a concentration of people is a potential target.
The plan doesn't have to be elaborate or take much time to develop. It's all about maintaining good situational awareness of your surroundings your location. Thinking, "I'm at X and if Y happens the nearest exits are at A,B, and C" might be an adequate escape plan. Just remember that as you move in your environment, the paths of escape may get longer and need to change.
If you are with your family, make sure that they know the plan too. I'll be honest that this is one step that I often overlook. Go over the general plan beforehand in case you become separated. Train them to develop the same "aware" mindset. It would also be helpful if you have a preset word or phrase to use in case something goes down so that you can all head to the appropriate escape path without having to explain what is going on.
I do this at work as a wildland firefighter. We have escape routes designated that we are to travel along to predetermined safety zones where we are safe from the fire. The same thing can be done while grocery shopping.
If there is no other option, then it is time to draw you concealed carry weapon (you do have your CHL, right?) and actively defend yourself and your family. Make sure your family is in as safe of a place as possible with plenty of cover. The last thing I'd want to do is draw fire towards my family. It might sound cowardly and/or selfish, but the safety of my family is my first priority and I'm not sure if I can risk them to save another. It also seems like these recent shooters have been pretty well armed with (in many cases) body armor of some type. It is probably a good bet that those of us that carry concealed don't have the firepower to contend for a extended firefight with someone armed with a rifle and/or multiple firearms. If I could figure out how to CC an M4, I would....
So there you have might thoughts: have a plan, if at all possible get out, if it comes down to it - draw your weapon and fight.
Keep your powder dry and please pay attention to what's going on around you.