How To Treat Red,itchy Cheeks And Rashes On The Neck?

My daughter has red, itchy checks and a slight rash on her neck. She also has bumps on her arms and legs. Her whole body is itchy and she does not have a temperature. She feels good but has a little bit of a headache. She has had the rash since yesterday. She is about 60 lbs and is 9 years old. She is in excellent health. What could this be?