Sure, you'd love if your 7-year-old had fewer sick days away from school. But what if by bolstering her immune system now, you could also protect her from developing serious diseases, such as cancer, later in life?

An attitude of wellness Tell kids they'll get sick, and chances are they'll live up to your expectations. "Instead of saying, 'Don't go outside without your coat—you'll get sick,' try saying, 'It's cold today; if you wear your coat and hat, you'll be more comfortable.' Give them a wellness attitude, and help them learn that they have control over their own health," says Jane Sheppard, publisher of www.healthychild.com.

"During childhood, when the immune system is still developing, there's a great opportunity to set the stage for improved health and resilience," says Joel Fuhrman, MD, family physician and author of Disease-Proof Your Child (St. Martin's, 2005). "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." Here's how to best support budding immune systems.

Nutrition
Favor fruits and veggies You've heard it before, but it's worth repeating: Fruits and vegetables offer a wealth of protective phytochemicals that enhance the activity and function of immune cells and protect against disease. In one study, kids who ate the most fruit had an impressive 38 percent lower risk of cancer later in life (Journal of Epidemiology and Community Health, 2003, vol. 57, no. 3). Berries, cherries, plums, and pomegranates are among the most powerful immune-boosting fruits. When it comes to veggies, eat more dark leafy greens, tomatoes, carrots, and cruciferous vegetables, such as broccoli and cauliflower.

You've got to love it "I used to be heavily involved in ballet, until it got really competitive and became a stressor in my life. Now I do what I want for exercise, and I do it because I love it. You have to enjoy it, or it won't be healthy in the long run. On some level, it has to feed your soul." —Stephanie, 18, Boulder, Colorado

Focus on high-quality foods
Emphasize the immune-building fruits and veggies listed above, along with whole grains and healthy fats, such as those found in nuts, seeds, and avocado, says Fuhrman. Avoid empty, sugary calories whenever possible because sugar depresses the infection-fighting activity of white blood cells, says Alan R. Gaby, MD, a nutritional medicine specialist. Even natural sweeteners, such as honey and juice, have similar effects when consumed in excess, he says. Conventional kids' snacks are notoriously full of empty calories, so try these healthy options: pomegranate and kiwi fruit salad; trail mix with raw almonds, dried cranberries and air-popped popcorn; or 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. "Whenever there is extra inflammation, the body has less available energy to keep the immune system functioning as well as it should," says Fred Pescatore, MD, author of The Allergy and Asthma Cure (Wiley, 2003). "It's like putting the wrong type of gasoline in the car; it hinders your performance." If you suspect your child has food allergies or sensitivities, seek guidance from your health care provider.

Herbs & supplements
Power up with probiotics
Probiotics can enhance immune function in children and are especially protective against allergies, diarrhea, and respiratory tract infection.

Probiotics optimize the immune system by stimulating infection-fighting white blood cells and reducing inflammation, says Gary B. Huffnagle, PhD, author of The Probiotics Revolution (Bantam Dell, 2007). To get more into your child's diet, start with yogurt: Serve with cereal; mix with mashed bananas and freeze in ice cube trays for a cool, healthy treat; or make smoothies with unsweetened yogurt and frozen berries. If your child won't eat yogurt, try a Lactobacillus acidophilus supplement; aim for 5 billion CFUs per day of lactobacillus or bifidobacterium.

Support adrenal function
Ashwagandha (Withania somnifera), an Ayurvedic herb, boosts immunity by supporting and balancing adrenal function, says John Douillard, DC, PhD, Ayurvedic physician and author of Perfect Health for Kids (North Atlantic, 2003). The adrenal glands produce cortisol, and overproduction of this "fight-or-flight" hormone can dampen immunity. Ashwagandha is particularly helpful for cold prevention during winter, but it can also be used whenever kids are stressed, exhausted, or run-down. For children 6 to 12, give 500 mg per day with breakfast; children over 12 can take 1,000 mg per day. Or give teens 16 and up a gentle homeopathic combo formula designed to support adrenal health, such as NatraBio Adrenal Support.

Stabilize hormonal changes
"Puberty and adolescence are marked by dramatic shifts in and surges of hormones," says Richard Shames, MD, author of Feeling Fat, Fuzzy, or Frazzled? (Plume, 2006). "This is monumental as far as the developing immune system is concerned. Because 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 8 to 18, aim for 100 mcg per day.

Lifestyle
Let them eat dirt
Well, not really, but don't get too protective. "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," says Jane Sheppard, editor and publisher of www.healthychild.com and founding executive director of the Holistic Pediatric Association. Avoid antibacterial soaps, cleansers, and gels; most contain triclosan, a powerful chemical that may contribute to the development of antibiotic-resistant bacteria. Instead, use a natural antibacterial gel like EO Hand Sanitizer, or make your own with witch hazel or alcohol, tea tree oil, and lavender essential oil.

Play! "For kids, the most important fitness activity is unstructured play, and lots of it," Douillard says. Vigorous play is critical for physical health and positive mental and emotional growth. Get your children moving with fun, unstructured activities like hiking, dancing, or playful games of tag. "Even half an hour a day is enough," says Douillard. "But if they're having fun, they'll play longer—and get more exercise."

Stay in the sun
"The sun is our primary source of vitamin D, which has broad effects on the immune system," Fuhrman says. "One theory holds that kids get more colds in the winter than the summer because they get less sunshine—not because they're indoors with other kids." Depending on your skin tone and the climate you live in, about 15 minutes of full sun exposure a day will allow the body to produce sufficient amounts of vitamin D, he says. If your kids have dark skin, or you live in a cloudy climate, they may need vitamin D supplements—at least 200 IU per day.

Laugh—long, loudly, and often
"You can give your kids the best food and nutrition, but if they have underlying sadness, their immune system will suffer," says Sheppard. "When you're happy, and when you laugh, your brain releases chemicals that increase immunity."

Lisa Turner is a Colorado-based health writer.