Missing Children's Assistance Act of 2002 - Amends the Missing Children's Assistance Act to: (1) direct the Administrator of the Office of Juvenile Justice and Delinquency Prevention to use the annual grant to the National Center for Missing and Exploited Children for purposes including coordinating the operation of a Cyber-Tipline to provide online users an effective means of reporting Internet-related child sexual exploitation in the areas of distribution of child pornography, on-line enticement of children for sexual acts, and child prostitution; (2) extend the authorization of appropriations through FY 2006; and (3) increase the authorization of appropriations for the annual grant to the National Center for Missing and Exploited Children for FY 2003 and to extend such authorization through FY 2006.