Bu giving him the local , seasonal and prebiotics rich foods and fruits . focus more on a well balanced home cooked food .

Breast milk has all the essential nutrients required. But, Aptamil gold formula milk has prebiotics and HMO. These also help in improving immunity and gut health.

If your baby is less than one year, It's better to continue breastfeeding as long as possible because that's the best. If you baby eat solid food you can give Well-cooked and pureed meat, poultry or beans. Ground, cooked, single-grain cereal or infant cereal with breast milk or formula. Cooked and pureed vegetables.

Babies when small don't gain weight that easily. And all babies are different from each other. Usually breast milk is enough to help with immunity. If u are looking to boost the immunity further you can give prebiotics rich formula milk like Aptamil gold it helps a lot.