The wagon is a pretty good idea for bugging out with the family and the price is definitely right. If if was in a similar position (which I am not) I would look into this BOB yak w/ setup options
Personally I will start with my jeep, then progress to my bicycles, then to my Bug out bag then to digging in and fortifying. In your case as in my case, forward momentum is the key to getting out of a situation. As long as you are able to make progress as fast or faster then the rest of the masses, you will likely be in better shape. You and your family plan are on the right track. Just remember that as you and your family evolve, so must your plan and equipment. Good luck on you venture.