My daughter has one on her lip. Because of the location (facial) we went to see a pediatric dermatologist at Children's Memorial. They specialize in hemangiomas and have seen kids nationwide. I'm very well versed in this topic! :) Below is a summary based on the literature I have from the hospital.
**Most are harmless.** The only time it can become an issue is if it causes challenges with normal bodily function (social challenges nonwithstanding). -For your son, I would pay close attention to whether his vision is obstructed as is grows.
Our neighbor had one on her chin and neck that had grown internally as well and swollen her trachea 75% shut. That was an extreme case.
All hemangiomas appear in the first month of life. All STOP GROWING by 8-9months of life and slowly begin to disappear. 50% are gone completely by 5 yrs of age. 90% are gone completely by 9yrs of age. (The rest eventually disappear completely, it just takes longer).
Depending on the severity, treatment may or may not be an option. My daughter's cannot be treated because it is too flat. The normal approach, a steroid shot, would cause a divot in the natural lip tissue. So we just have to wait for hers to go away on it's own.
Severe cases (the neighbor, listed above) are treated with a cardiac drug called Propanolol. The child is admitted and tested to make sure they can withstand treatment healthily, and the drug is administered. The hemangioma begins to disappear VERY quickly. (Neighbors is almost completely gone, 3mos later).