I can remember one of the first times I handed my professional camera to a 3 year old and the reaction on the parents face. As many times as I have done this over the years (knock on wood) none has ever been dropped. Children usually understand the value of what they are holding and seem to be quite careful.
There are two things that consistently happen when letting kids use "adult cameras". First, they feel a sense of empowerment and secondly they become part of the process, which is especially helpful if part of your goal is to photograph them. Here are a few pictures from a recent brunch where we passed the camera around the table and everyone got a chance to take some pictures. These were all shot with the Nikon 7000 and the Tamron SP 17-50 f2.8 taking advantage of the available light and f2.8 aperture. I bet you can guess who shot who.