There are two possibilities for what your grandson has. One is the possibility of a parasitic cyst
. This is very common in children and fits
in with the location and it is usually just under the skin and will feel hard. The other possibility is one of a sebaceous cyst. These are swellings that arise from glands just under the skin. It would be really helpful if you could take a picture of the swelling and send it to this site or to me. Please do not be too anxious as it is very likely to be a simple swelling with a simple solution. Please feel free to contact me if you need any clarifications.
Dr Antony Robert C
Columbia Asia Hospitals,