Kelly Clarkson's using the oldest parent cliché in the book ... telling her kids they can't use social media as long as they live under her roof -- 'cause what she says goes, period.

The singer/mama-of-two dished out her somewhat strict parenting rules in a new interview with People -- explaining why it's her way or the highway when it comes to social media and her children. Namely, they ain't allowed to get on the 'Gram ... or anything else.

She says, "[Social media] can be really hard on kids in general but especially kids with parents in the public eye. So I have informed them they’re not allowed to, under my roof, ever have [it]." Kelly adds things may change down the line, but for now ... hell no.

One interesting part of the interview ... Clarkson talked co-parenting with her ex-husband and seemingly took a shot at him in the process -- which jibes with their contentious uncoupling.

KC says ... "My daughter was like, ‘Well, what if Dad lets me?’ I’m like, ‘Well, you’re there four days a month. Enjoy that.’ And right now he’s not letting them do it either."

Whether it's an intentional shot or not, she seems to be saying her daughter River and son Remington aren't seeing much of their dad these days ... at least that's what we can glean.

As we reported ... Kelly filed for divorce from Blackstock back in 2020, and it was finalized nearly two years later. She also took him to court over how he managed her finances -- and there, too, some interesting nuggets emerged about their professional relationship.

Don't worry Clarkson kids ... only about a decade until you're out of social media jail!