A.F.
From a quick google search, my daughter's birthmark is not a nevi/nevus but I did notice that as she has grown, the coloring has thinned some which also makes it appear that small freckle type dots are showing up.
Her birthmark has always been pink, and the freckle-type dots are reddish, but I assumed it was because the skin was stretching and the color was stretching with it.