Ok, couple of quick things.. ss already mentioned the crop (good call there). I wasn't able to see the EXIF data on Flickr for this, so not sure what Aperture/Shutter Speed settings were used. The focus looks pretty good, for portraits you really want to focus on the eyes if you can and it looks like that part worked out pretty well. Looks like you got the camera down to his level as well, which is great, a lot of folks have a tendancy to shoot down when shooting kids.
The two things I would probably recommend - first would be a different color background, the one your using appears to be a light brown and as a result really not as much seperation between his hair/skin and the background. I think a little more seperation here would make for a stronger image overall. The second would be the lighting, a fill flash or adding another light source somwhere off to his right to soften some of the shadows on the right side I think would also probably improve things overall.
But all in all I think it's a very good image.