Suggest Home Remedy For Itchy Red Rash On The Body In Kids

hello,doc. my son 31/2 yrs old having itchy and it look red rash all over his body what is the good home remedy to cure my son,but he don't have fever,i already give him allergy medicine this morning around 7 am,is it fine if i could give him again the allergy medicine its's already 9 pm now,please help me.thank's grace