What Causes Rashes On Face And Chest Of A Child?

Hello I have a 2 year old son.He had a fever for 2 days and went away and now has a rash for 3 days now..It seems like it moves..He has it on his face and chest and behind his knees but it comes and goes.He had a bug bit on his wrist before the fever.Can be be allergic to the 7 week old kitten that we got 2 weeks before the fever and sach started