Kids have to be 12 or 13 years of age; whatever the age they have to be to use the fitness room (that's what I heard the CM tell a parent who had a child that was one year younger than the minimum age).
They walk really fast. The guy walks faster than the girl (sorry, don't remember their names). I did it twice when I stayed at VGC in April; once with the girl and she was a good walker & talker (I was able to keep up with her). The second time (a few days later), got the guy and I couldn't keep up.