Children are not small adults in relation to exposure and vulnerability. Rapid growth, development, and anatomical and physiological changes in various organs and organ systems differentiate children from adults in relation to exposure and vulnerability to environmental exposures. The unborn child and lactating child may be exposed to environmental pollutants that depend on the maternal exposures. Also children are exposed to different levels of environmental agents because of the size and developmental stage. Children may experience different sources of exposure because of behavior, for example, eating sand from a sandpit, exposure to dust while crawling on the floor. Moreover children have a longer life span in which to express illness. Second, children are particularly dependent on their environment and on their caregivers to make the right decisions for them. Their ability of making independent decisions and giving their consent to participate in research depends on their age, may differ from adults, and their consent to participate may be reassessed as they grow.