Peanut allergies mean that your body is misguided when it identifies certain proteins. Instead of recognizing that peanuts are safe, it thinks they're dangerous. When you consume a peanut protein, your immune system sends out an antibody called immunoglobulin E to attack it. The antibody then releases other chemicals and you end up with an allergic reaction, probably with some unpleasant symptoms attached.
Peanut allergies are particularly prevalent among kids. Unlike some other ailments that children suffer from, peanut allergies aren't contagious and can't be caught from other kids at kindergarten. It's not exactly clear why some children develop peanut allergies and others don't. There are a few known factors that come into play, however. One of them is family history. If other people in the child's family have allergies, there's a stronger chance that he'll have allergies -- as opposed to kids who have no family history of food allergies. Another factor in the development of peanut allergies is whether a child already has other allergies. If he's allergic to another food, he's more likely to develop a peanut allergy than if he isn't. Even if he's allergic to pollen or some other airborne allergen, he has a stronger chance of getting a peanut allergy than a kid with no allergies at all. Age is considered a factor in developing peanut allergies, too. Younger kids are more likely to get peanut allergies since their immune systems aren't fully mature yet; once they mature, they often recognize harmless allergens as harmless and stop reacting. However, peanut allergies are one of the allergies that are tough to outgrow.
To verify whether your child actually has a peanut allergy, a trip to the allergist is in order. An allergist can do skin tests and blood tests to check which allergen triggers a child's symptoms -- and whether it's an allergy at all. Sometimes, food intolerance is mistaken for an allergy.