Thank you for your query,
Your child is having gastroenteritis
and developed diaper rash
due to frequent passage of stools and long exposure to the loose stool
that present in the diaper.
Maintain his hydration by giving oral rehydration solutions like Pedialyte, lemon water and coconut water and monitor his hydration status by looking his urine output, activity and skin turgor.
Frequently change diapers and at home avoid wearing diapers.
Clean the area with a soft clothe after washing with clean water and gently touch and dont wipe, allow the area to dry and apply a bland ointment of nappy rash containing zinc oxide
to make a protective barrier.
Consult your Pediatrician
for further management.
Hope I have answered your query.