Birhmarks with knots

My 19 month old grandson has had a purple looking birthmark on his left side upper chest near his under arm.  He developed the birthmark about a month after birth, and has seem to have grown some.  He has more than one in the same area and now is starting to develope small knots under the birthmarks about the size of half a grain of rice.  We have been referred to a dermatologist, should I be concerned?