The teenage son of "Teen Mom" star Jenelle Evans is hospitalized after running away once again, and this time Child Protective Services is taking custody of Jace ... TMZ has learned. Sources with direct knowledge tell us, Jenelle's 14-year-old son ran away from his grandmother's home Saturday, and wasn't found until 11:45 PM Sunday. Jace had previously run away from Jenelle's home several times and was placed under the care of Jenelle's mom, Barbara. Our sources say Jace is now in a hospital, and CPS will place him in foster care as he's run away so many times. Our sources say Jace, was recently busted for vaping at his school ... and when grandma found out, she took away his phone. We're told Barbara had been advised by Jenelle, CPS and the foster care team not to give Jace a phone in the first place, but she thought he could handle it. When Barbara took the phone away as punishment, we're told Jace split, prompting this latest search for the teen. Running away has become a trend with Jace ... as we've reported, this is at least the fourth time he's run away from home ... including the time in September when he slipped out a window on the same day Jenelle's husband, David Eason, is accused of roughing him up. Remember ... Jace spent most of his childhood in Barbara's care, but Jenelle regained custody earlier this year, only for him to run away from home a bunch of times, and end up at Barbara's house again. As we told you a couple weeks ago, Jace is keeping his distance from Jenelle and David. Our sources say CPS officials are exasperated by the case -- they're worried about Jace, but at this stage, if he gets in any more trouble, he could end up in a juvenile detention facility.