My Son 2 Years Old ...has These Bumps On His

My son 2 years old ...has these bumps on his tailbone in a cluster . Then also in a line more bump on his left butt cheek. He also has one bump right were his underwear line is . They look to be the color of his skin .they're a little red though . They don't look like pimples . No blisters . Just bumps . He has had the. For a year started out small and is now spreading to the one butt cheek and spot on his underwear line . What could it be ?