Soft swelling on top of scalp

Patient: SirYesterday, I noticed a soft swelling on top of scalp of my son, aged 6 yrs after a fall against a wall. It is of about 4X2 inch in size and feels as if filled with some fluid. It is not paining significantly. He did not have any usual symptoms such as vomiting, bleeding, nausea etc. He seems fully normal playing, eating. It might be from some earlier injury which he did not tell us. I shown him to a local doctor. He told to apply ice pack and further local fomentation and wait for five days. But I am worried although he seems absolutely fine. Please Help.

Symptoms: Soft swelling on top of scalp