YETITIME, sorry to hear about the crash that your daughter had. I feel her pain because that's what happened to me.
See, I started riding and the learning curve was steep in the beginning. So, feeling good, I started to get aggressive -- going faster and faster and adding a hop here and there. It felt great when I stayed on the bike, but it only took one bad crash for me to realize that I went ahead of myself. I did not know how to do corrections at speed yet and panic braking was still the second nature.
I guess what I'm trying to get at is: it's easy for a beginner to get ahead of herself when everything is going smoothly. So, maybe some crashes at low speed (e.g. trackstand) are a good thing -- it helps you realize that crashes CAN happen. Oh, that, and a set of protection gear. I got my elbow and knee pads from SportsMart (well after I got my stitches). I like them because they are not very bulky and I can wear them whole day. Plus they inspire confidence. Hope your son grows to enjoy mountain biking.