The appearance seems to be normal. It is mostly due to erupting permanent molar. The swelling and pain will eventually subside but if your child complains of excessive pain, give him a painkiller syrup according to his weight. In case you find that there is no relief, get an XRAY done for him.
Next Steps
Visit a paediatric dentist if the pain does not subside within three days of giving analgesic syrup.
Health Tips
Massage the area with a clean finger.
Give him semi solid food and a soft diet which will not impinge on the affected mucosa.