Jenelle Evans & David Eason Family Outing in Las Vegas

Jenelle Evans and her ex, David Eason, were under the same roof in Las Vegas this week ... but don't read into it ... 'cause TMZ has learned it definitely wasn't a romantic reunion.

Witnesses tell TMZ the "Teen Mom" star hit up Yard House at Red Rock Resort Tuesday night, and she wasn't alone. We're told Jenelle was there with her young kids ... and yes, David was in the mix too.

But before anyone jumps to conclusions ... witnesses tell us the vibe between Jenelle and David was anything but romantic. We're told the two acted "kinda cold" toward each other throughout the outing ... keeping things distant despite sharing the same table.

A rep for Jenelle tells TMZ ... the meetup is strictly about co-parenting ... emphasizing the two are not back together romantically.

This all comes amid ongoing family tension involving Jenelle's son, Jace. As we reported ... Jenelle's mom, Barbara Evans, believes Jace has been struggling, especially with limited communication. Barbara told us she's been checking in daily and asking staff at his treatment facility to reassure him she's okay.

We're also told Jenelle has also been in contact with Jace, including visiting him at the facility during spring break.

The situation follows an alarming 911 call last month, when Barbara claimed Jace had a gun to his head ... an incident that led to him being placed in treatment.

As we reported ... a judge denied Barbara's request for emergency custody, but the fight's far from over. Barbara told us a temporary custody hearing is set where she and Jace's father, Andrew Lewis, plan to present evidence.

Meanwhile, Jenelle's camp tells us she spoke with Jace over the weekend and says he's focused on improving himself.