Does yor son complain of headache, vomiting/loss of consciousness(symptoms of head injury
) ?Any bluish/ bluish black discoloration of the swelling? Any bleeding around the eyes or behind the ears? If any of the above symptoms are present , take him to the doctor IMMEDIATELY .
If it is just a swelling of the eyelid with no other symptoms, you can adopt a wait and watch policy and if it doesn't get better in a day or two, take your son to the doctor . Have a nice day :)