What Causes Fever And Pimple Like Rash In A Child?

My boy who is 28 months young has had a few colds this past season; he s got well for a few days and then meets a sick kid and gets sick again. this time three days ago he shared a frozen chocolate covered banana with his cousin who was sick, coughing and runny nose; withing 12 hours he had the same symptoms. he is had fever, dry cough, clear runny nose, and pimple like rash around his knees, inner thighs mainly but also a few around his calves, and elbows. he was feverish the second night, and all that day; day 3 he seemed okay; went to the park played. this morning he had fever again. the pimple looking rash looks reddish; not scratching; we re using witch hazel and body lotions. Just wondering if I should be more concerned?