My youngest son, whom we shall call Nub, stopped walking suddenly and refuses to put any weight on his right foot, but will only crawl from place to place.
Since he is unable to tell us what's bothering him, we took him to the doctor's. Not entirely conclusive, but seems like he has a sprained ankle (or something). It's entirely possible, given his loose ligaments for something like this to happen.
My poor baby!
It doesn't seem to bother him much, other than not walking. Kids are pretty smart: if it hurts, they don't use it.