We never like to see our movie stars “trying too hard” in a screen comedy. But sometimes, the effort itself is worth a few laughs.

I mean, they’re suffering for their art, trying to wring laughs out of thin material, adding value, giving the studio paying them fair value, no matter how silly they look doing it.

“Playing with Fire” takes wrestler turned action star (“The Marine”) John Cena where Vin Diesel (“The Pacifier”) and Dwayne “The Rock” Johnson (“The Game Plan”) have gone before.

Put this prime slab of action hero machismo in a scenario that forces him to deal with little kids, and fail. Haplessness and hilarity ensues, right? Except that it rarely does.

It’s a topical comedy about the heroes of the moment — Smoke Jumpers, the elite parachutist firefighters deployed into blazing forests, saving lives and homes as they struggle to contain the consequences of drought-stricken forests in a hotter, dryer and “changed” climate, and people who like to live in the middle of such tinderboxes.

Jake Carson (Cena) is station superintendent (“Sup”) in the woodlands of Redding, California, a no-nonsense firefighting son of a legendary fire fighter who died in the line of duty.

He’s got no time for flirting with the cute biologist (Judy Greer) obssessively studying toads by the lake down the mountain, and no time for shenanigans, even though Keegan-Michael Key, John Leguizamo and the lumbering “Lurch” of a fireman, “Axe” (Tyler Mane) are his kinda-goofy crew.

“Where’s my REDDING CREW AT?” he bellows.

“EVERYWHERE!”

That changes when he has to airlift three kids out of a blazing cabin, and the weather and the weekend means nobody can come take them off he and his Redding crew’s hands until Monday.

He’s just had the other half of his crew quit on him. There’s a big promotion coming, with the super-hero-sized division commander (Dennis Haysbert, having a laugh) about to retire. The last thing Jake needs is unruly, unmannered kids messing up his firehouse, playing with his fire extinguishers and flare guns, demanding bedtime stories.

The kids — played by Brianna Hildebrand, Christian Convery and Finley Rose Slater — are unrestrained, unschooled, prone to pilfering and petty vandalism. Well, not little Zoey (Slater). She’s the lovable one.

He may think of himself as “a father figure, only way cooler.” But Jake’s about to learn a hard lesson.

“Kids. You can’t control them. You can only contain them until they burn themselves out.”

“Race to Witch Mountain” director Andy Fickman finds most of the movie’s laughs via slapstick — detergent accidents, oil spills, flares and fire extinguishers used IMproperly.

The funniest sight gag might be Jake’s attempt to pull the kids out of that burning cabin via helicopter. Rodrigo, the pilot (Leguizamo) keeps misunderstanding Jake’s commands, yanking him up into the ceiling — hard — over and over again.

Key and Leguizamo mug for the camera and trip through some grownup one-liners. Rodrigo is from “San Quentin.” Can’t tell the kids what that really is. “A small college in Vermont” is the quick explanation Mark (Key) comes up with.

A running gag is Rodrigo’s quick way with a homily or anecdote, and inability to process the facts of his quotes.

“As Lance Armstrong once said, ‘That’s one small step for man. And WATCH out for the next one!”

Cena is a funny guy, as he’s proven in “Trainwreck” and those kiddie “Fred” movies of about ten years ago. Here, he’s got too little to work with, even if the poking the uptight guy is the surest way to laughs that there is.

Attempted one-liners aside, the only character and performance to generate giggles is Mane’s turn as the always axe-toting “Axe,” a lumbering menace who turns out to be a soft touch around toddlers.

Everybody else — the sprightly Greer included — tries too hard. Because they have to.  Every wrinkle in the plot is nakedly contrived, an obvious screenplay convenience. Every gag is given away. Every one-liner vanishes into the void.

Kids may love projectile poop gags, but even they should be able to smell the odor “Playing with Fire” puts out there.

MPAA Rating: PG for rude humor, some suggestive material and mild peril

Cast: John Cena, Keegan-Michael Key, Brianna Hildebrand, Dennis Haysbert, John Leguizamo and Judy Greer

Credits: Directed by Andy Fickman, script by Dan Ewen, Matt Lieberman. An Nickelodeon/Paramount release

Running time: 1:36