Jenelle posted a bunch of TikTok videos Saturday, claiming her eldest son is now in her custody. As you probably know, Jenelle's mom, Barbara, has had custody for years.

Jenelle said, "I have custody of Jace. He lives with me now full-time.  My [3] kids are happy, they're healthy. That's all that f***ing matters."

She went on to talk about how "stupid" she was as a young woman and all the mistakes she made, including with men ... but now, she says, things are very different.

Barbara tells TMZ she still has full custody of Jace. She got custody a decade ago when Jace was just a baby, because of Jenelle's erratic behavior. Jenelle has only had visitation rights ever since.

Barbara says Jace has recently been going back and forth between her house and Jenelle's due to the pandemic ... Jace goes to Jenelle's house for 3-4 days at a time, in part just so he has a change of scenery. He'll go over there to do his schoolwork ... then he comes back to Barbara's.

Barbara tells us she called Jenelle after her daughter announced she regained custody, and Barbara says Jenelle told her she "misspoke" and recognized Barbara still had custody.