Fine art indeed. I love seeing well-done realism on Newgrounds.
The kid in the back's hair comes off his head kind of a lot. Mentally draw the line where his skull is and check the hair. I may be wrong on this, though; I've seen kids with high hair before.
That same kid's left eye, to our right, is just a tiny bit higher than the other one. It took me a long time staring to pick that out, though.
Lastly, and I add a disclaimer to this one that I'm terrible with light and shadow, how is such intense red being reflected on the back kid's shirt? Does the front kid's shirt glow? Or is this some aspect of lighting that I'm not aware of.
It took me awhile to pick out those three tiny things. There may be more, but I'm not skilled enough to pick them out if there are. Awesome work, overall. You must have put a ton of time into this, and whoever's buying it won't be disappointed.