Children's Mercury Exposure Act of 2007 - Requires the Secretary of Health and Human Services (HHS): (1) acting through the Director of the National Institutes of Health (NIH) and in consultation with the Administrator of the Environmental Protection Agency (EPA), to establish a program for research regarding the risks posed by exposure of children to mercury from contaminated industrial sites; and (2) acting through the Director of the Centers for Disease Control and Prevention (CDC), to study and report on the prevalence of such exposure. Authorizes the Secretary, acting through the CDC Director, to make grants on a competitive basis to state departments of health to conduct testing of exposed children.