The girls often come from impoverished rural villages and are sent to the city to work wealthy homes, where many report being verbally and physically mistreated. Half of the report's sample had dropped out of school, while a third had never attended.
A law regulating domestic workers has been under development since 2006 and the government has promised it will be on the 2013 parliamentary agenda.
Morocco was singled out over underage maids because the phenomenon appeared to be more widespread than in other countries, with girls starting work at even younger ages, said Becker.
Sarah Lee Whitson, Human Rights Watch's Mideast director, however, said the government has been responsive to the group's findings.
"The cooperation we've had with the Moroccan government in discussing these issues and sharing ideas about these issues is in many ways a model on how Human Rights Watch should be able to work," she said.