Instead of a kid's radio flyer wagon, take a look at nursey wagons, the kind of wagon that you use to cart around plants, bags of mulch etc. Bigger, much more stable, more durable wheels, better capacity. Inflated, ball bearing wheels, decent steering. I think bugging out with one of these would be a last resort, but could haul someone a good distance with mobility issues and maybe a kid or two. I've seen decent models at Home Depot for $100-150, and models in catalogs with mountable side rails. Our neighbor has one and I've pre-requisitioned it to move immediate casualties after a quake.