He gets awful eczema which seems to be triggered by soap. My inlaws know this. They had him for the day at the weekend and when I picked him up he was soaked in soapy water (they hadn't even changed his top) and now his arms and torso are red raw again.
He enjoys playing in soapy water and I know they let him because it keeps him busy for hours.
Would I be unreasonable to just outright ban soapy water play? Also, how would you politely but firmly word such a ban?