The main differences between caimans and crocodiles are caimans’ smaller size, pointier head and upper jaw covering their bottom teeth. But that’s hard to tell from a paddleboard when all you see are menacing, beady eyes. And it’s hard to explain to your kids wobbling next to you.

We’re on the Rio Mora in Costa Rica’s Tortuguero National Park and while caimans are commonplace, SUPs aren’t. According to our guide Reinaldo, these are the first SUPs the soulless, reptilian eyes have ever seen.

“It’s okay,” he says to my daughters, Casey, 12, and Brooke, 16. “We’re bigger than they are so they’re afraid of us.”

“Yeah, and I’m bigger than you,” Brooke chides Casey.

We continue upstream, taking a tiny fork to the right. Howler monkeys screech overhead, flinging from branch to branch. Slaloming through vines and ducking under giant frond leaves, our path is finally blocked by a 250-year-old mountain almond tree. It fell, says Rey, just two months ago, and its wood alone is worth $30,000.

It’s these and other indigenous hardwoods, as well as the world’s largest green sea turtle rookery, that led to the region’s preservation in 1978. Located in a maze of jungle-lined rivers along the Caribbean, Tortuguero is one of its most heralded national parks — the perfect place, I reasoned, to instill an environmental ethos in my kids from the perch of a paddleboard. While most people get to it via motorboat, my friend, Rafael Gallo, had a better idea: Take paddleboards to it for the first time ever, down an 8-mile-long, remote tributary.

At our put-in on the Rio Suerte, we unloaded a mix of SUPs and kayaks and began our paddle to Mawamba Lodge on the park’s outskirts. The jungle’s charm quickly took hold. Spider monkeys, the second fastest tree monkey in the world, launched overhead above yellow trumpet flowers and daisy chains of heliconias illuminating the green banks.

Two hours later we entered a fresh water estuary paralleling the Caribbean from Nicaragua and paddled to lunch on the bank. A boardwalk hike through the selva quickly prompted Casey to whistle the bird song from the Hunger Games.

A viper, toucan, poisonous red dart frog and hand-sized, golden orb weaver spider later — its web is the strongest in the world, synthetically emulated to make bulletproof vests — we made the final push to the lodge, whose green roofs emerged around a corner. A covered dock housed a fleet of motorboats used by its more conventional-arriving guests.

Built in 1985, the 40-acre, 56-room lodge was one of the first established in the area. An open-air bar, porch hammocks and pool with bridge and waterfall quickly sent the kids scrambling. But its best feature is its location, sandwiched on a jungle spit between the freshwater estuary and the sea. It’s a five-second hike to Caribbean waves on the east, and a mango throw from the fresh water of Tortuguero to the west.

Owner Maurizio Dada clearly follows his government’s conservation ethos. That afternoon, we toured the lodge’s bio-digester, which heats the rooms’ hot water with human waste, as well as the “ranarium,” or frog farm, and butterfly pavilion filled with blue morphos and zebra longwings. The country has 10 percent of the world’s total butterfly species, and Maurizio hopes to keep it that way.

Walking back through a forest of paprika, avocado, lime, coconut, guava and other trees, we saw a three-toed sloth lounging high in a tree, prompting Brooke to ask for one as a pet. While litter box upkeep might be a snap – they poop only once a month – our cats remain safe.

At the bar, the kids basked in virgin piña coladas while we settled for soda and cacique, a local, triple-distilled sugar cane liquor. With the lighting hitting the witching hour, we loaded the boards on the motorboat and shuttled out to the river mouth. When the sun radiated a wall of green under a flock of white egrets, we paddled over to where the freshwater met the crashing waves of the Caribbean.

Waking to a cacophony of bird calls, we find local critters having breakfast before us. High in a guava tree, the mouth of a green vine snake wraps around the head of a clay-colored robin, Costa Rica’s national bird. Next to it, an iguana the size of Casey’s leg placidly gnaws a leaf.

Fueled by thick Costa Rican coffee, we motor to the park office for our 8:30 a.m. entrance slot. Heading south toward Panama, we turn up a tributary bordered by towering walls of foliage. A caiman submerges with a flop of its tail in the same lily pad we set the boards in. “Dad!” my daughters yell in unison.

Taking idle strokes down the Agua Fria, we witness a log standoff between a caiman and orange-eared slider turtle — Mayweather vs. Pacquiao played out in the jungle. Casey startles a Jesus Christ lizard, so named for its ability to run on water, using its tail as a rudder. Humans, says Rey, would have to reach 80 mph for such an escape. Plunging in to cool off while exploring myriad waterways, we eventually make our way back to the lodge. At sunset, on water matching the magenta of the sky and seashell smooth, we paddle to the roadless community Tortuguero for what Casey’s eyed all trip: a coconut with a straw.

Pulling up to kids at the dock, we stash our boards, take in a pick-up soccer game on a palm-lined field and stroll through town with its “Don’t worry, be happy” Caribbean vibe. Locals play cards at a park table, kids zing around on rusted bikes and dreadlocked Rastas mill around in Bob Marley shirts. We find Casey her coconut and watch the sky turn blaze pink. We toast Tortuguero and the experience of seeing it from a SUP. When I ask Casey what could be better, she emits a caiman smile, “Maybe if I had this coconut on a paddleboard.”

—Info: http://www.riostropicales.com, http://www.mawambalodge.com