I like the desat. I think what it is lacking is contrast. As Kashi said the attention goes to the bike part in the lower right. That seems to have the sharpest focus and the most contrast. I'd like to see more contrast in the eyes and smile with sharper focus there. Perhaps a High Pass layer with a mask would do it. I like the square crop and the composition, and the joy of a boy with his bike.
I'm not sure the desaturation was a good idea here. As kashi said, the "different" thing that grabs your attention is the green piece, not the smile. I'd suggest trying it without the desat and with most of the bottom cropped off. The spokes convey "bike" without needing the gear shaft.
I'm not crazy about the desat though - puts my focus on the green piece instead of the eyes.
Cutting one eye in half seems to be a no-no around here too.
You got a 7 from me - I quite liked the unique take on a portrait, and I'm a sucker for bike shots and great smiles. I'm really very surprised by the sub-5 score, to tell the truth. I don't know if it would have worked better in color?