Tomatoes, Eggplants, Cucumbers
Children who regularly load up their plates with these veggies, along with green beans and zucchini, are nearly 40 percent less likely to develop symptoms of allergies and asthma compared to kids who rarely ate them, according to a study published in Pediatric Allergy and Immunology. The exact link is not known, but Scott H. Sicherer, MD, an associate professor of pediatrics at Mount Sinai School of Medicine, believes explains that these antioxidant-packed, so-called "fruity-vegetables" may protect your body's cells from everyday damage, which makes the immune system healthier. When the immune system's in check, it's less likely to attack foreign substances in food, triggering an allergic reaction.

Fish
The same study found that children who ate the most omega-3-packed fish had fewer allergies and were less likely to develop asthma by age 7. This follows research revealing that children of women who ate more fish during pregnancy also had reduced asthma risk. "The fatty acids in fish like salmon are believed to boost the immune system by reducing inflammation," says Sicherer.

How soon to introduce fish to your kid's diet? Most children can start after they're comfortable with other solids like cereal and veggies, but check with your pediatrician first. He may suggest waiting longer (especially for shellfish) if your infant already has allergic problems or if there's a strong family history of allergies.

Stick to low-mercury fish like salmon and trout; avoid high-mercury types like swordfish, king mackerel, or tilefish. Tuna is safe in limited amounts; keep your child's intake to one ounce of light canned tuna a week for every 12 pounds he weighs (a 36-pound toddler could safely eat half a can a week, for example).

Nuts
Children age 7-18 who eat nuts at least three times a week are less prone to wheezing, found a study recently published in the journal Thorax. This healthy snack is packed with vitamin E, an immune-boosting antioxidant, as well as magnesium, a mineral that may reduce asthma risk. Got young kids? To reduce choking risk, chop nuts up completely or only serve them to children over 4, advises the American Academy of Pediatrics.