It looks like a cataract to me, with an eye infection the eyes would be watery and you would see white discharge in the corner of the eye. It could also be he scratched his eye, but once again the eye would be watery and it doesn't look to be in this pic, hard to tell. Cataracts can sometimes be treated with eye drops if you start early, and if it's caused by a scratch you need to treat it right away before it scars, so worth getting checked out as soon as possible.