K.S.
Vitamin D3 (we also buy the children's gummies at Target).
Multivitamin
Plenty of sleep
Lots of handwashing - especially before eating or after being out in public.
My son also takes Echinecea/vitamin C if he is starting to get the signs of being sick.
Healthy diet with lots of fruits/vegies/wholegrains, limit sweets and processed food, limit artificial dyes.
Massage also helps stimulate the immune system and flush toxins.
Plenty of water, limited juice and soda
Age 3 is tough because they are getting exposed to a lot but usually don't have much immunity yet.