How can a 4-year-old child with low immunity enhance it?

Patient's question:

Age of the child: The 4-year-old baby has very low immunity. Since birth, they have not been breastfed and have been drinking formula milk. Currently, they often catch colds, have diarrhea, and require long-term intravenous treatment each time.
History of treatment and effectiveness: No treatment has been administered. Unsure how to improve immunity.
Help needed: Want to know how to enhance immunity.

Doctor's answer:

How to Enhance a Four-Year-Old Child's Immunity—Basketball Shooting
Adults can first teach the baby to practice stationary shooting. The height of the basket can start from 20 centimeters above the baby's height and gradually increase. Additionally, adults can practice together, incorporating movements such as running, jumping, and catching the ball.
How to Enhance a Four-Year-Old Child's Immunity—Jumping and Hopping
Even when walking, young children love to jump and hop. Therefore, parents should also cater to this natural tendency. Encourage the child to play simple games like kicking shuttlecocks, jumping rope, and hopscotch. This not only exercises the body but also helps in the child's physical development.