Damon and his wife, Luciana Barroso, hit up the Italian restaurant Toscana in Los Angeles with their kids Sunday night ... where BFF Ben tagged along for the family night out.

Ben's facial expression was notably neutral, but he did have a discernible pep in his step as he made his way into the hotspot.

Ben kept it casual for the dinner, wearing jeans, sneakers, a white T-shirt and a tan button-down ... not drawing too much attention to himself.

Matt rocked a black polo and dark jeans, color-coordinating with his wife ... who wore an all-black ensemble.

Matt was photographed beaming inside the restaurant -- keeping things cheery, not letting any relationship woes bring his best bud down.

Ben seemed to have a good time with the Damon family ... he was even heard laughing alongside the valet while grabbing his car after the meal.

Maybe BA was just happy to have the company ... since he's been ordering takeout for most of his meals lately.

Still, Ben doesn't seem to be sweating his divorce proceedings. TMZ broke the story ... J Lo filed for divorce from Ben last week ... filing the docs at L.A. County Superior Court, where she listed April 26 as their date of separation.

We're told there's no prenup ... and no settlement has been locked in yet, either. So, there could still be a legal battle ahead.