If Faith Evans knows one thing about Stevie J it's that he's good -- really, really good -- at making babies, and the newlyweds definitely have baby fever.

We got Faith and Stevie talking for the first time about their surprise Las Vegas wedding. They insist the hookup is NOT a publicity stunt, and explained why they decided to go all the way.

The R&B duo's heard some of the negative reaction to their marriage, but say they're ignoring all the haters. As we reported, some family members are pissed they didn't get a heads-up.

They got really excited though when we asked if they plan to have babies. You gotta see Faith declare her baby factory is open for biz. 

As she put it, we all know Stevie can make it happen ... with 6 kids of his own already.

Looks like they got in a damn good dress rehearsal while shooting the "A Minute" music video.