Jenelle Evans' teenage son, Jace, has been keeping his distance from his mom and her husband, David Eason ... and we're told the kid's happier now than he's been in a long time.

Sources with direct knowledge tell TMZ ... 14-year-old Jace has zero contact with the "Teen Mom" star and David, as he's been living with Jenelle's mom, Barbara, while he remains under custody of Child Protective Services. Sources say Barbara also isn't in contact with Jenelle or David.

TMZ broke the story, David was charged with child abuse in a case involving Jace ... allegedly roughing up the teen and causing "marks on the right art and left and right side of the neck," according to court docs.

The docs also say Jace's injuries weren't sustained by accident ... and the date of the alleged incident was the same day Jace slipped out his bedroom window and ran away from home.

We're told Jace is glad to be back living with his grandma ... and the place feels like home to him. Jenelle just regained custody of Jace earlier this year, so he's really spent most of his childhood in Barbara's care.

He also recently enrolled in a brand new school after being out for the past few months. You'll recall, he was reported as a runaway after getting in trouble at school back in August.