Hello H J,
Most probably your child is having Scurvy, due to vitamin C deficiency.
It requires therapeutic dose of Vitamin C drops, 100 - 150 mg three times a day for a week and then daily maintenance dose of 50-75 mg once.
You could also apply any gel over gums containing glycerin etc for pain and irritation. He should not have any grainy or coarse food yet. Teeth may be cleaned with soft brush dipped in warm saline water.