The latest trend in baby food is bacteria  -- the good kind. This month, Nestlè unveils a formula with probiotics, live cultures that can boost digestion and immunity. It joins a growing list of probiotic-enhanced foods for kids (think Dannon's Danimals). Meanwhile, Beech-Nut is now offering the first jarred baby food with prebiotics, substances that nourish the growth of good bacteria already in your child's gut. But can these products really keep your child healthier?

The jury's still out on probiotic-enhanced foods. More research is needed, says the American Academy of Pediatrics (AAP). "Though probiotics can't hurt, it's not clear that adding them to food actually boosts long-term health," says Frank Greer, M.D., the head of the nutrition committee at the AAP. Since these foods also tend to cost more, a switch may not be worth the expense  -- especially not after age 1, when experts say the body's flora can only be changed temporarily. But talk to your doctor if you're considering probiotics to treat an illness; studies show they can reduce colic and diarrhea when kids are already sick.

Prebiotics are a better long-term bet, says Dr. Greer. They increase the probiotics already in the body, instead of introducing new bacteria that may or may not work. Plus, Beech-Nut's line costs the same as traditional versions. You can also try Horizon Organic's Baby Yogurt or Stonyfield Farm's YoBaby, which have both pre- and probiotics.