I agree with Corinne, You need to find out exactly what type of birthmark your son has and that you also need to see a ophthalmologist to find out if the birthmark is involved some how in the eyes.
The V-Beam Pulse Dye Laser. To get the most info on this laser go search it on MSN or googles. It would be able to explain it allot better then I would.
I have used the V-Beam on my PWS and it took 15 minutes and if you have looked at any of my pictures in the PWS section you will see that it is allot larger then your sons. I bet it would only take about 5 minutes or less to do the treatment. There are ways to go around having your child go under GA. They have numbing creams that work wonders. If you want more info on it you would have to email me email@example.com
Talk to you soon.