Trouble keeps coming for Chief Keef -- according to TMZ, he's being sued for child support. And worse, the girl who's suing him is still in middle school.

The unnamed girl says Keef impregnated her in 2011, when he was 15. There's no word on exactly how old she was at the time. According to Illinois law, Keef could be charged with a misdemeanor, because it's technically illegal for two people younger than 17 to have sex, but that would happen only if the girl's parents pressed charges.

As we reported last week, Keef was just sent to juvenile detention for 60 days for a violation of his probation.

Will this kid ever get his act straightened out?