Well, generally speaking, there are many causes of droopy eyelids. For example, weak levator muscle, paralysis of some nerves, even Injuries such as fracture of the skull bone between eye socket and nose can cause droopy eyelids. So you should pay attention to it. To treat it, there are some ways you can have a try. For example, you can just put the teabags in the refrigerator until these become cool, and then just apply them on your eyes. Repeat this for a few days. Also, proper and moderate exercise including eye exercise can be effective. You can just put a finger under the eyebrow and lift it slowly and hold it on that position for ten seconds before bringing the eyebrow back to its normal position. By the way, rubbing your eyes will lead to droopy eyelids. So just stop it.
Droopy eyelids is known as ptosis, is the abnormally low position of the upper eyelids. It can happen to one eye or both eyes, which is sometimes called to be lazy eye. Without timely and proper treatment, droopy eyelids might gradually go worse, covering pupil and iris which might lead to other eye conditions, such as amblyopia or astigmatism. Because the droopy eyelids could interfer with vision, it might cause headaches and brow ache for straining all time to elevate eyelids during reading, writing, or watching TV. As to the causes of droopy eyelids, it varies a lot from case to case. Someone is born with it, which means it can be hereditary. Someone gets it as he/she gets aging. It can be caused by trauma to eyes too. The trauma injured the muscle which raise eyelids so the eyelids get droopy. Sometimes it can be caused by eye surgery. We don't what situation of your son is in. You could see whether any cause fit your son's situation. The only treatment for droopy eyelids is surgery. Because the droopy eyelids won't get fixed by themselves overtime, actually they will get worse and worse, so why don't you talk to your doctor to see if surgery could be adapted for your son. Wish you and your son good luck.