Overview: "Children's toxicology", a renovating study field of irreversible "early exposure-delayed effects"

"Children are not small adults". This is a well-known phrase, especially in the clinics for diagnosis, efficacy of treatment, side effect, and prognosis. However, in the field of toxicology, this issue has long been a challenge. The knowledge has been limited to the differences in metabolism and other physiological factors. Currently available test guidelines for fetuses and immature animals are teratogenicity and reproductive toxicity studies. These tests look for straight-forward (essentially macroscopic) outcomes established within a rather short period of exposure to the test substances. However, recent advances in molecular toxicology allow combination of in vitro and in vivo studies at molecular levels. The target molecules and receptors can be identified in quantitative fashion and at the fine structure levels around and below the resolution of normal light microscopy. Such expansion of the knowledge lead us to consider a rather new category of "receptor mediated toxicity" or "signal toxicity". Such non-organic insults would merely induce transient effects on adults. However, there are growing evidences that such slight insults on the developing and maturating organisms can leave irreversible effects that become overt in adulthood. As an overview, toxicology has entered a new phase where children's toxicology becomes a renovating study field of the irreversible "early exposure-delayed effects".