Red bumps with small white blisters in the center

My 21 month old son has several flat red bumps that have developed under his nose and around the area of his lower face.  It seems like the bumps apear when he wakes up either from a nap or from sleeping all night.  The bumps start out red with a tiny white blister in the center.  Then after a day or so the blister disappears and the redness stays for a few days then goes away.  The ones directly under his nose have small scabs.  This has been happening for almost a week.  Some are going away but others are still coming.  What could this be?  Should I take him to the doctor?