you need antihistamines, like piriton, that should calm and stop it. cool baths, cool clothes, not water proof suncreams. i always keep a bottle of piriton in, that will sort it very quickly - you may need to use some kind of antihistamine through this heat to keep it at bay. speak to your chemist or GP. how old is your child? piriton can cause drowsiness. there are other antihistamines available but piriton is very fast working in an emergancy.