Thank you for your query on Healthcare Magic.
The rash could be due to an allergic rash
The cause of allergy
could be a newly introduced food, soap, or clothes.
Observe for the causative factor.
For rash, you can apply a calamine
lotion externally over the rash twice or thrice daily.
If there is itching, you can give an oral antihistamine in prescribed dose.
Consult the pediatrician
for examination and for medication advise.
Hope I have answered your query.