What Causes Red Bumps On Elbows,knee And Wrist In Children?

My 4 yr old son has red bumps on his elbows and bottom that look like pimples. His twin brother has them on his bottom as well, but his seem to also be between the fingers and much smaller. They both have random bumps on a knee or wrist. (Just appearing within the last day) Both boys have been recovering from a fever, cough and cold. They both attend the same preschool and my son (with the cluster bumps on the elbows, has autism and is highly sensitive to touch and and will touch his face for sensory issues). The bumps don t seem itch or bother them in any way. I have been using a hydrocortisone cream and keeping the bumps covered. They have never had this and I am confused. please Help