Raised bumps on son's back leg - not warts or bug bites but can't figure out what they are. HELP

My 4 year old son has raised bumps on his right back leg. Some are large and some are tiny but all have a white head on them. He's had them for about 6 months now but they never hurt until recently. I thought they were warts but had not treated them. They recently have turned red/inflamed. He says they've started to hurt and when I put cream (from local health store) on them, he says they hurt to the touch but the cream makes them feel better. I've searched the net but can't figure out what they are.  One of the bumps is hard under the skin and doesn't have a white head (so it may be a different issue all together).