As many people saw during the SB celebrations ... Jason famously wore a Chiefs luchador mask to Super Bowl LVIII after-parties in Las Vegas after his brother Travis Kelce won the big game.

As it turns out ... the mask actually belongs to Elijah Smith, an 8th grader from Dallas who gave Jason the mask for a photo op -- but who never got it back amid all the post-game chaos. JK himself had recently said he found it on the floor ... in any case, it's the kid's.

Anyway ... Jason had already pledged to get Elijah his mask back in a social media post Friday morning, and we've since learned the NFL player has contacted Elijah's parents.

Sarah Smith, Elijah's mom, tells TMZ … Jason personally reached out to them Friday while Elijah was at school, and he plans on calling back so he can talk to Elijah on the phone later at some point this weekend.

The Smiths tell us Jason came off as very thoughtful, kind, and apologetic ... and they told him there was no rush in returning the luchador mask, especially given the Super Bowl parade shooting tragedy in Kansas City.

Sarah explains that Elijah's a pretty superstitious teen -- as lots of sports fans are -- and believes the mask is a lucky charm of sorts, which is why he wants it back.

In his post on X, Jason agreed ... "Your mask indeed brings great fortune, I owe you big time, sorry it was commandeered."

Worth noting -- the family isn't upset Jason got to wear it after the Super Bowl instead of Elijah ... they say all the videos and photos of Jason in Vegas with the mask are absolutely "epic." Once Jason returns the mask, Elijah's mom predicts her son will wear it to Chiefs games next season ... unless he frames it, of course.