Answer: Accordingly to you ,yes baby is underweight according to the age. So , first of all give variety of foods if non veg then give varieties in nonveg like chicken soup, egg wraps etc for proper gain but if pure veg increase the protein and fat products in baby diet.
You need to maintain the routine and daily food chart for the baby that includes all the necessary nutrients needed at this age.
Include carbohydrates,vitamin,protein, iron and calcium . Yes fat is also needed.
Weight gain is not a one day task it needs consistency and acceptance . How the baby body is performing. First thing is you should check the baby appetite.does he/she feels hungry and offcourse the hemoglobin level. If everything is in range than build interest in food. Take the baby to park, social gathering where you can feed the baby. Never leave the house without carrying the snacks that includes some wraps, smoothies or normal fruit bowl. Baby eat in front of others more nicely than at home. Be creative in your cooking side and presentation side. Feed the baby on the place where you generally have your meal with proper decorated plate. The items that you can feed are :
Rice Apple porridge, rice kheer, Apple kheer, ragi kheer, sabudana kheer, ragi and banana porridge,Apple ragi porridge, ragi pancakes, ragi idli, ragi and nuts porridge, moong daal soup,potato carrot soup, tomato carrot soup, muesli curd, muesli and milk , vegetables soup, sooji banana porridge , sooji Apple porridge, scramble eggs, oats and nuts porridge, Apple oats porridge,milk oats and dates porridge, daliya, Apple daliya porridge, banana daliya porridge, barley kheer, curd oats, plain and veggie khichdi, upma, sooji chilla, veggie appam, sabudana vegetables khichdi, makhana kheer , boiled vegetables with pasta and breads, chicken soup, etc .
Apple puree, chikoo puree, papaya puree, carrot puree,pumpkin puree,watermelon, kiwi puree, banana puree, banana with curd,avocado puree, home made flavoured yogurt.
Banana shake,dates shake, Apple shake, avocado shake, kiwi shake,chiku shake , Banana kiwi smoothie, avocado Apple smoothie etc.are the options .