There is no specific formula that makes babies chubbier. However, there are some major ingredients you should look out for if your baby's weight is not optimal. The main ingredient is fat. Yes, fat is essential in the diet of infants. It is one of the main constituents of natural breast milk because it is important for the development of the brain and the nervous system. Also, it aids in the easy absorption of essential vitamins. The importance of a fatty diet for babies cannot be overemphasized as they need it very well at that stage in their lives. So, parents should shun foods that have little or no fat for their infants as these foods won't help development areas that are much needed leading to underweight babies apart from other potential issues.