My 25-month old daughter is the same. Her body weight is always out of chart. Her PD asked us to give her Pediasure as well. But my D didn't take it that well (diarrhea). So we changed to carnation breakfast. It's a powder-like nutrient food supplement. You can buy it from most of the grocery stores (narmally placed in the breakfast food section).
As long as your son is healthy, I wouldn't worry that much.
As long as your son is healthy, I wouldn't worry that much.