what do i give to my child to keep him from getting sick all the time?

My child is 4 years old and just started school. He is getting sick all the time- runny nose, coughing, sneezing. What are some remedies/foods that will make him well and prevent him getting sick all the time?

increase his immunity.

Lots of vitamin c…oranges are a great source…give them an orange with breakfast and lunch each day and or use vitamins…