Rapper Chief Keef -- Sued for Child Support

17-year-old rapper Chief Keef is already getting a head start on his baby mama drama -- in fact, he's already being sued for child support.

The woman filed the petition for child support in Chicago, claiming Keef -- real name Keith Cozart -- fathered a baby daughter with her back in 2011.

The woman's exact age is unclear, but according to the docs, she currently takes classes at a Chicago middle school.

Cozart -- who has since worked with Kanye West, Young Jeezy, and Rick Ross -- was 15 at the time.

The woman is suing Keef for an undisclosed amount of child support, including health insurance and other medical expenses. Calls to both Keef's people and the woman's family were not returned.

Keef's no stranger to legal problems -- he was just sentenced to 60 days in juvey for violating his probation on a gun charge.