Hello,
Without examination,confirmation of a diagnosis is tough but it sounds like eczema to me. It is a form of chronic dermatitis (rash).Allergic reaction is one of the important causes of eczema. Allergic reaction can occur to strong soaps, Solvents, chemicals, certain foods, food additives, plants, metals, cosmetics, even urine and faeces of some animals (dust mites).
Wash the areas several times with fresh water. Do not use any cosmetic products at the sites. You can apply some calamine lotion at the rash as it will help in soothing the skin. He can take some OTC oral antihistamine medications like Benadryl or Claritin and see if it helps but make sure to consult his pediatrician before trying any medicine.
For mild-moderate eczema a weak steroid may be used (e.g. hydrocortisone as dermacort), whilst more severe cases require a higher-potency steroid (e.g. clobetasol propionate, fluocinonide).
Eczema can be exacerbated by dryness of the skin. Use good quality moisturizers to prevent moisture loss from the skin.
Hope it helps.Take care and pls do keep me posted if you have any additional queries.Kind regards.
Try diaper rash cream like Balmex or A&D. It will heal and soothe at the same time.