Totaling a car is simply an insurance term. It can range from a bent frame (on an older car - not worth fixing) to a catastrophic accident. Sounds like the OP and his/her kids are fine, otherwise the OP would have mentioned it.
That said, Subaru's are solid vehicles, but the Acura MDX is larger and higher.
Right now you're desperate for safety, but take a deep breath. The safest thing you can do is keep your head on a swivel. Unfortunately, kids in the back can be a massive distraction, and may cause you to take your eyes off the road. Resist this temptation, but if you can't, pull over to the side of the road or a parking lot. Pulling over will have a dramatic effect on children's behavior.
