No one would propose putting children in a situation where they will definitely be hurt but teaching them to manage risk is extreamely important.
Most rockclimbers don't know what to do with loose rocks or how to manage them, but this is the way all cliffs are in the beginning. For example, the Palisades and road cuts can be loose. When I first started climbing it was on a lot of basalt. On basalt cliffs you start at the top and work your way down first removing all the loose rocks. On some rock you need to do this every year. When you get to a handhold on basalt you need to look for cracks to understand what you are holding on to, if it is a loose rock. If it looks questionable you don't play with it, you don't test it out, you leave it alone. The reason for this is, if you test it and then it comes loose then you may not be able to hold it in place. If your are going to test it be prepaired to drop it. But this is something that needs to be done from the top down, and with a spotter on the ground with communication.
Climbing, like race car driving, is really an adult sport. Unless it is a climbing gym.
Rock Climbing in Hawaiihttp://www.youtube.com/watch?v=kvTHeBJ_gkAhttp://www.youtube.com/watch?v=afI58PRmTJ0&feature=related
The Mohonk Mountain House and the Mohonk Preserve have done a great job protecting the environment thus far, but ... it's all down hill from here http://youtu.be/9AU8fMo8v4k.