Chief Keef -- The Kid Is My Son, the Kid Isn't My Son ... I Can't Decide

Chief Keef's got a brand new baby mama situation -- she says she just had his son ... his lawyer says take a number, lady ... and Keef can't decide whether to celebrate.

According to docs filed in Kentucky ... a woman named Lauren wants CK to pay child support for her 2-month-old baby boy, and lists him as the daddy.

Sources close to the situation tell us they met last year at one of his KY shows, then he flew her to Chicago a few times -- and yada, yada, yada ... baby!

Keef actually posted a photo of the boy Monday with the caption, "The White Sosa" (referring to his nickname) and then deleted it after an hour. Our sources say Lauren sent CK the pic, and he hasn't met the kid yet. In the docs, Lauren says she hasn't seen Keef since conception.

Keef's lawyer says Lauren's claims are untrue, and the rapper's constantly targeted by women looking for easy paydays.

Apparently the lawyer forgot about this story ... and this one.