The commonest cause of vaginal itching and/or discharge in this age is VAGINITIS due to either improper clean up wiping from back to front or allergic reaction to the water, soap or toilet roll used in cleaning up.
To know the specific cause for your baby and for appropriate treatment kindly see a doctor preferably a paediatrician for further evaluation and management.
Expecting? Start Tracking your baby's development week by week below
Paediatrician