Hi My Son Is 2 Years 5 Months And He

hi my son is 2 years 5 months and he still is 11 kg... I am worried about his weight I am giving him ostocalcium syrup and tonoferon drops but not regularly ...suggest what all and can I give him.... another thing I just want to know if I can add any supplement with milk as he does not drink milk at all so I have to feed him by a bottle when he sleeps....