We’d love it if our kids had fewer sick days away from school, but what if by bolstering their immune systems now, we could also protect them from serious diseases going forward?

“During childhood, when the immune system is still developing, there’s a great opportunity to set the stage for improved health and resilience,” says Dr. Joel Fuhrman, a family physician and nutritional researcher in Flemington, New Jersey, and author of Disease-Proof Your Child. “A healthy diet and lifestyle can help kids avoid common childhood illnesses like colds, ear infections and allergies, as well as ensure greater resilience against disease later in life.”

Focus on High-Quality Foods

Fruits and veggies have a wealth of protective phytochemicals that enhance immune cell function and protect against disease. In a study published in the Journal of Epidemiology & Community Health, kids that ate the most fruit had a 38 percent lower risk of cancer later in life. Berries, cherries, plums and pomegranates are among the most powerful immune-boosting fruits. For veggies, eat more dark leafy greens, tomatoes, carrots and cruciferous vegetables such as broccoli and cauliflower. Also emphasize whole grains and healthy fats such as those found in nuts, seeds and avocado, advises Fuhrman.

Sugar-laden calories depress the infection-fighting activity of white blood cells, says Dr. Alan R. Gaby, of Concord, New Hampshire, author of the textbook, Nutritional Medicine. Even natural sweeteners such as honey and juice have similar effects when consumed in excess, he says. Try healthy options like pomegranate and kiwi fruit salad; trail mix with raw almonds; dried cranberries and air-popped popcorn; and hummus with red pepper strips and baby carrots for dipping.

Pinpoint Allergies

Food allergies and sensitivities can suppress the immune system by increasing inflammation in the body and call for consultation with a health specialist. “Whenever there is extra inflammation, the body has less available energy to keep the immune system functioning as well as it should,” says Dr. Fred Pescatore, a New York author of The Allergy & Asthma Cure. “It’s like putting the wrong type of gasoline in the car; it hinders your performance.”

Shore Up with Supplements

Tell kids they’ll get sick, and chances are that it’ll happen. Instead, nurture an attitude of wellness and help them learn they have control over their own health.

Probiotics can enhance immune function in children by stimulating white blood cells and reducing inflammation, says Gary B. Huffnagle, Ph.D., a University of Michigan Medical School immunology research professor and author of The Probiotics Revolution. They are especially protective against allergies, diarrhea and respiratory tract infection.

Start with yogurt: Serve with cereal; mix with mashed bananas and freeze in ice cube trays for a cool treat; or make smoothies with unsweetened, non-dairy yogurt and frozen berries. Or consider a Lactobacillus acidophilus supplement; aim for 5 billion CFUs per day of Lactobacillus or bifidobacterium.

Ashwagandha (Withania somnifera), an ayurvedic herb, boosts immunity by supporting and balancing adrenal function, says Dr. John Douillard, Ph.D., a Boulder, Colorado, chiropractor, ayurvedic physician and author of Perfect Health for Kids. The adrenal glands produce cortisol, and overproduction of this “fight-or-flight” hormone can dampen immunity. Ashwagandha is particularly helpful for preventing colds and can also be used when kids are stressed or tired. For children ages 6 to 12, give 500 mg per day with breakfast; children over 12 can take 1,000 mg a day.

Stabilize Hormonal Changes

“Puberty and adolescence are marked by dramatic shifts in and surges of hormones,” says Dr. Richard Shames, of Sebastopol, California, co-author of Feeling Fat, Fuzzy, or Frazzled? “This is monumental, as far as the developing immune system is concerned. As the immune system is directly linked to hormonal influences, any hormonal imbalance will affect overall immunity.” Shames recommends selenium—a potent antioxidant and general immune booster—to help balance hormones. For children ages 8 to 18, aim for 100 mg per day.

Let ’em Get Dirty

“Once a child has been exposed to dirt and germs, the immune system responds by trying to expel those bacteria from the body, which strengthens immunity,” counsels Jane Sheppard, owner of HealthyChild.com and founding executive director of the Holistic Pediatric Association.

Avoid antibacterial soaps, cleansers and gels; most contain the chemical triclosan, which some researchers suspect of contributing to development of antibiotic-resistant bacteria. Instead, use a natural antibacterial gel or make one, by combining witch hazel or alcohol, tea tree oil and lavender essential oil.

Stay in the Sun

“The sun is our primary source of vitamin D, which has broad effects on the immune system,” Fuhrman says. “Depending on your skin tone and the local climate, about 15 minutes of full sun exposure a day will lead to natural production of sufficient amounts of vitamin D.” If kids have dark skin or live in a cloudy region, they may need vitamin D supplements—at least 200 IU per day.

Laugh Out Loud

“You can give your kids the best food and nutrition, but if they have underlying sadness, their immune system will suffer,” remarks Sheppard. “When you're happy and when you laugh, your brain releases chemicals that increase immunity.”

Lisa Turner is a Colorado-based health writer.