“Chupa” is a harmless Spanglish trifle for kids, an “E.T.” riff about Mexico’s flying (!?) vampire bobcat of myth, El Chucacabra.

It’s built on a simple formula — kid discovers a supernatural (or extraterrestrial) playmate, must save it from those who would exploit it — and executed accordingly.

There’s a little pop to its casting and limited charm in its Mexican cultural touchstones. Look at this list of screenwriters and see if you can guess how “limited” that is — Sean Kennedy Moore, Joe Barnathan, Marcus Rinehart and Brendan Bellomo. Not a Spanish surname in the writing of this Chris Columbus (“Home Alone”) production.

Evan Whitten (his grandmother’s Mexican) plays Alex, a Kansas City kid who lost his Mexican-American dad and has come to resent his culture, thanks to bullies at school. So his Mom (Adriana Paz) sends him South, to San Javier, to visit his abuelo, “Granddad” to him because Alex knows no Spanish.

He’ll hang with his cousins — the non-English speaking Memo (Nickolas Verdugo) and bilingual tween Luna (Ashley Ciara) — pick up the language, the culture, the cuisine (“Crickets? Those are BUGS!”) and live on grandpa’s ranch for a week or two.

Here’s the first place “Chupa” goes right. The great Demián Bichir hurls himself into this grandpa role, a retired, brain-injured luchadore who will teach the kid about his heritage, and maybe show him a few wrestling moves in the bargain.

The second boon to “Chupa” is its villain. Christian Slater is Indiana Jones’ evil twin, a scientist paid by wealthy moguls to prove a Chupacabra exists, and catch it so that it’s blood’s “healing qualities” can be exploited for material gain.

He’s close to success before Alex shows up, just missing catching one in the film’s prologue. But when CGI baby Chupa gets separated from his mommy, Alex finds and befriends him and stands in Quinn the Scientific Poacher’s way.

“Stop being so dramatic, kid. Go home. Get a DOG.”

Slater brings just enough amoral panic — Quinn’s got a deadline — to make his villain register.

But Bichir, whimsical as forgetful grandpa — all bellows and bravado remembering his former life, as masked hero of the luchador ring, El Santo — just brings it. He is a hoot to behold, and gives the film a cultural authenticity it lacks in most every scene he isn’t in.

There isn’t much to this that will appeal to anybody over the age of eight. But the film’s real sin is in how it shortchanges the legend and the Mexicanness of all this.

Director Jonás Cuarón, who co-wrote “Gravity” with his acclaimed director dad Alfonso and who directed “Desierto,” had better credits and better chops than most anybody listed as a writer, and real credibility in the culture. Paying him to give the script a more serious going-over could have paid real dividends, in this case.

Instead, all he’s here to do is make the kids hit their marks so that the CGI critter will fit in the frame. Pity.

Rating: PG

Credits: Evan Whitten, Ashley Ciara, Nickolas Verdugo, Christian Slater and Demián Bichir.

Credits: Directed by Jonás Cuarón, scripted by Sean Kennedy Moore, Joe Barnathan, Marcus Rinehart and Brendan Bellomo. A Netflix release.

Running time: 1:39