That red birthmark on your baby could be a (harmless) tumour

A haemangioma is actually a tumour and can grow rapidly, however, it is harmless and will usually go away on its own. — TNS

A haemangioma, also known as a strawberry birthmark, is a bright red birthmark that shows up in the first or second week of life.

It looks like a rubbery bump and is made up of extra blood vessels in the skin.