Cheeses for the vitamin k2 mk4/mk7, magnesium, calcium, Food rich in bone building stuff like calcium, magnesium, trace minerals, some hard-ish enough food to chew on, steak and chicken should be decent, you dont wanna wreck his teeth from hard food, nose breathing and proper tongue posture. Vitamin d from the sun and get some supplement if you feel hes getting not much of sunlight. Use toothpaste with nano hydroxyapatite to help cover up cavities while its still new.Gargle some water after sugary stuff so they wont build up gunk for the bacteria to hold on to.