My son has a hemangioma close to his eyelid. We have been to several birthmark specialists(due to its location) who have said they reach their max size @3-6 months then @1 year they start lightening and flattening til they are 3.5 years old when they are completely gone. Since your sons is on his calf I don't understand your concern. It isn't harming him and it's not in a spot where it could cause any disfigurement. If it is growing still at a very rapid rate I would ask your doctor if treatment is necessary since there are all different forms.
My LO also has similar marks, he has some light marks on his eyelids and forehead that darken when he's angry or straining. He also has it on the back of his head/neck and a small strawberry like spot on his right upper thigh. Doctor said nothing to worry about and will probably go away as he gets older.
I had the same red mark on my forehead as a baby that darkened when I cried. It went away long ago.
thank you for all your replies I was just wondering because the dr said the one on her calf in rare occasions can cause excessive growth in that leg because of the enlarged veins. I've decided to take her to a specialist. Thank you.
Re: vascular birthmark
I had the same red mark on my forehead as a baby that darkened when I cried. It went away long ago.