what you have described seems to be contact dermatitis
This occurs due to reaction between the tender skin and moisture around scrotum
. They can be aggravated by
1. The chemicals we are using for bath and washing clothes
2. The water itself which we use for the above two purposes.
Inadequate exposure of air will aggravate the problem.
Dry him well. Apply coconut oil in the morning after bath and again in the afternoon time.
Do not use diapers for more than 4 hours
No synthetic materials
If there is intense itching or pus formation visit the doctor
Once in six months deworm the child