What vitamins can i give 21m old to prevent sickness/ help build immune system? she has started daycare and seems to be sick all the time.

Doesn't help: Supplements or vitamins would only be helpful if the kid was deficient in their diet.They do not "boost" anything & end up in their urine within a day.The average preschool kid will have 5-7 URI's & 2-3 episodes of diarrhea/yr. After an initial break in period, they often settle into less frequent illness. Home solo care cuts the numbers some but not by much.