A healthy immune system is a result of a balanced diet. Make sure your child eats enough of antioxidant-rich fruits and vegetables including oranges, carrots, spinach, bell peppers, green beans, etc. Additionally, pay attention to the health of their gut, which requires a healthy diet of probiotics and prebiotics. Yoghurt, buttermilk, bananas, oats, and other foods are excellent for boosting the beneficial bacteria in the gut.