Although in terms of chemical exposure children are simply small versions of adults, in other ways they are very distinct. Children's metabolic rates are different, their immune system in certain ways remains immature and rapid cell division of developing organs and tissues makes them more vulnerable to chemical and carcinogenic assault. Very young children (2-3 years of age) have distinct hand-to-mouth activity which exposes them orally to toxics that older children and adults are not exposed. Lead is one example of this, there being a great distinction between blood lead levels in younger children compared to older ones. Young children are also prone to asthma and allergies, which not only affect them at the time but can predispose to further problems, including respiratory problems when one gets older. This section will specifically focus on and serve as a listing site for all issues that directly affect children in terms of toxic exposure and chemical injury.