Nice! Guess, he is normally more happy than on the pics!
Your sculpts are quite severe. Maybe, it is your taste, but at least in case of a child you could aim for a more relaxed and smooth expression.
I would smooth everything a bit, except a few rims of the lips, eyes and nose.
the rim of the lips should be a bit more curved.
To change the expression a bit more modify the edges of the mouth with the grab tool.
The lower part of the eyes and the part below it could be better. Compare the right picture of your son with the left picture of the sculpt.
Maybe, the eyes could be a bit smaller, as well.
When portraying such delicate features it could benefit from sculpting the raise of the eyeball in the area of the iris.
http://de.academic.ru/pictures/dewiki/65/Augapfel.jpgThe inner part is a bit bigger than in the sculpt.
