There are many causes for photosensitivity( sensitivity to light) in adults and children. One of the commonest causes and probably where an eye exam begins is the refractive error or spectacle power. This is especially true in kids with a cylindrical number where the patient typically sees objects distorted in one meridian. So a point source of light looks like streaks and causes a glare which explains his aversion to bright light. In adults, its oncoming car headlights at night that are particularly bothersome. In kids, due to powerful eye muscles and the ability to mask small refractive errors, they seldom complain of bad vision. Also, they dont really know they cannot see perfectly. An eye examination done with dilating drops reveals such hidden refractive errors in kids. Your son needs one of these even if you believe he can see well. There are other causes for photosensitivity like an infection on his eye lids and eyelashes in the form of flaky white material like snowflakes seen in the region common again in kids that cause irritation in the eye when they fall in and lead to light intolerance. In this case, you will probably notice him rubbing his eyes a lot and blinking often. These are the commonest and are easily treated, the former with spectacles and the latter with eye drops and ointments.