Principles of adding complementary foods to infants: Babies can start adding complementary foods appropriately from 4 to 6 months after birth to meet their growth and development needs. However, there are some principles that need to be paid attention to when adding complementary foods. First of all, complementary foods should be added gradually. Do not add too many or too complex foods at one time, otherwise it may easily cause indigestion or allergies. Secondly, choose fresh, hygienic and nutritious food.