Wheelchair/ Crutch Relay
Borrow a wheel chair and crutches from a local agency.
Set up a course for the families to try, with obstacles to go around. The first stage of the race, one member of the family could use the wheelchair through the course. Next, hand off to another family member who must do the same course on crutches. Switch back and forth until all have gone through the course. See which family can do it the fastest.