YG and Baby Mama are Pregnant with Second Child and It's Another Girl

YG and his baby mama are back at it -- the couple's expecting their second child together, and TMZ's learned their daughter is going to have a little sister!

Sources close to the rapper have confirmed with us ... YG's baby mama, Catelyn Sparks, is pregnant with a baby girl. We're told she's due this summer ... sometime in July.

The 2 have one child together already -- their 3-year-old little girl named Harmony.

YG and Catelyn have a couple of baby registries, like most expecting parents -- at Buy Buy Baby and Target -- and it's pretty much what you'd expect ... strollers, pacifiers, baby bottles, a rubber duckie -- you get the picture.

One more fun fact -- we're told DJ Mustard's baby mama, Chanel, who's also pregnant and due very soon, has been Sparks' companion to several maternity classes -- and that's ON TOP of each already having 3-year-old girls. We know the fellas like to hang out together too.

Best wishes to both sets of moms and dads!