my baby is 4 kg at the time of a birth now she is 18 months old and her weight is 9 kg how to get gain weight

A. Practically your childhood have been somewhere around 12 kg at the age of 10 months looking at the birth rate of the child so your child is quite behind the expected weight gain right now at the age of 18 months your child should be somewhere around 13 to 14 kg can you kindly check with your doctor in this regard