I don't have children, but I can tell you that as a kid, if I fell and got hurt, my mom would make sure that it was nothing serious before cleaning it up and putting a band-aid on it. I am sure I would do the same with my children when I have them. Good question though!
I watched it closely for a little while. It was tempting to take them every time, but who can afford it? So I would watch it and see if they could move it at all. If the pain was severe with no relief, I took them in right away.