First, clean and wash the wound gently with a quaternary soap like normal (regular) Lifebuoy soap and water fifty times.

Do not cover the wound as the rabies virus dies on contact with air.

Did the dog bite without provocation? Can that dog be identified and tied up for observation for ten days? 

If he bled from the wound, then it is a Class III bite. Please arrange for Post-exposure Rabies Vaccination. The new vaccines are given in a small dose intra-muscularly in the arm or thigh. Anti-Tetanus Vaccine may also be given if your son's normal immunization schedule has not covered it.

He will require a painkiller. Please consult your Paediatrician.

the bite of the dog can give rise t disease called rabies which is 100% fatal. so the priority is to prevent from the disease. get the vaccination done. as the bite is on the site of a finger joint the teeth might have entered into the joint space. so get it examined by the doctor preferabbly a surgeon and a orthopadecian. it might require opening of the joint and debriding and than suturing. the doctor who examines will decide the appropriate next step

A BITE WOUND FROM A SUSPECTED RABID ANIMAL SHOULD NOT BE SUTURED, especially in the first 48 to 72 hours as there is a danger of driving the virus deeper into the body tissue !