Can we increase the height of children through diet or is it genetic?

Genetic: If he's in the very low percentiles, a lab workup to rule out growth hormone deficiency is a good idea. For all other reasons though, height is genetically determined. A good, healthy diet will ensure he meets his genetic predisposition. Otherwise nothing will change his final height.

Usually genes: There is no exercise, special diet, or other such plan to increase the height of anyone.A healthy lifestyle with proper exercise, nutrition and sleep habits will assure that a kid reaches their genetic potential. Improper diet/lack of sleep/long term illness/ lack of exercise may all contribute to less than expected final height.