Consider the full frame (as always). Personally I feel that the photo is about determination. His strong expression tells the story. Not seeing his feet makes the photo looked cropped.
Looking at it again I agree with you. I went back to check and it looks like that's the way I took it. I was shooting with a telephoto lens at the time and I either intentionally did it or I just wasn't far enough back to get the full frame. I'll try to reshoot it as you suggested, I think it would be better. Certainly won't be hard to have him find another tree to climb now that he's gotten his first taste of it!
I love climbing and it all started with trees. If you really wanted to get silly, leave the tele in the bag. Personally I go with a 17-35 (Actually it is a 28-50 or something on the D1). I like to get close to the subject. I also question the quality of the image with all that glass in front of it. Then again that may not hold true with modern technology.
But dont you have to be carefull about shooting children, unless they are your own.
Obviously it dont affect me much cause im 16...but if im taking a pic and there is a kid in it, I make it obvious I aint shooting them by moving the camer away....some people dont like it.