my daughter is 11.9kg now ..her birth weight is 2kg..she is active in all activity.. children in underweight is any problem

A. Buy the age of 3 1/2 of years a child should be a minimum of 15 KG so you can see video child is a lot behind that wait criteria so that is definitely a matter of concern I would say that you can consult a nutritionist and go ahead with a diet plan which is going to be healthy for your child to increase the overall weight and growth and gain of your child