In a pub by the shores of Loch Ness in present day Scotland, two young tourists pause at a framed picture of the creature alleged to live somewhere deep beneath the surface of the loch. The grainy “Surgeon’s Photo,” as the image is known in real life, was debunked long ago. But in “The Water Horse,” a new film opening Christmas Day based upon “Babe” author Dick King-Smith’s novel, the picture is a hoax of a different color. Hailed by a garrulous, and for the moment anonymous, local played by Brian Cox, the two Americans take seats while the man spins a yarn detailing the photo’s fictional origin some 60 years ago.

Our narrator explains in a fatherly burr that in the early days of World War II, “the Germans had captured the rest of Europe” and Scotland’s prospects were not looking good. Young Angus MacMorrow (Alex Etel), whom we meet on a loch-side outing, has a few things in need of sorting out as well. Angus believes his father to be away at sea with the Royal Navy. His pragmatic, secretly grieving mother, Anne (Emily Watson), knows otherwise. Deathly afraid of the water and yet drawn to it, and missing his father’s fanciful enthusiasm, Angus scrambles around the rocks and tidal pools at the edge of the loch. Angus returns home to the highland manor house that Anne runs for an absentee upper-crust owner, and discovers that a large barnacle-encrusted stone he quietly brought back from the shore is actually an egg. The egg yields an energetic, alternately feral and affectionate sea creature that Angus names Crusoe after Defoe’s castaway. Knowing that his no-nonsense mother would not take kindly to adding an unidentifiable and ravenous animal to the household, Angus takes great pains to hide Crusoe. Naturally, the arrival of Captain Hamilton (David Morrissey), in command of a British artillery company to be billeted in the house, and a new hired hand named Lewis Mowbry (Ben Chaplin), complicates things substantially.

Crusoe’s insatiable appetite and accompanying colossal growth spurts make him increasingly difficult to hide. When Mowbry accidentally discovers Crusoe, he identifies the beast as a “water horse,” an animal of Celtic legend that when ridden by a human “either carries him across the loch or drags him down to the bottom to his watery death. I can’t remember which.” The moment of truth arrives when Angus, forced to release Crusoe into the loch at Mini Cooper size, is reunited with the massive, full-grown, fierce, and digitally rendered animal now towering over the lad’s rowboat. “This isn’t so bad,” Angus cries out after taking a spin on and under the loch on Crusoe’s neck. “It’s fun, actually.”

And so it is. Thanks to a surprisingly nuanced adaptation by screenwriter Robert Nelson Jacobs (“Chocolat,” “The Shipping News”) and director Jay Russell’s magnanimous shepherding of his ingratiating cast, “The Water Horse” is that rarest of nearly mythic non-Pixar film creatures — a children’s movie that won’t have adults sneaking peeks at their BlackBerries.

While the digital effects that bring Crusoe to life are perfunctorily impressive (especially as many of the film’s most effects-laden scenes are rendered in daylight), the lingering strength of “The Water Horse” is its replication of a very lived-in and imperfect past and an overall willingness to collide with some of the grimmest facts of life head-on. “There’s no monster, there’s no magic,” Anne bitterly yells at Mowbry and Captain Hamilton just a few scenes short of being climactically proved wrong. “There’s just this war and death and people acting insane!” Her pain is as real as Mowbry’s disenchantment, the Captain’s creepy upper-crust machismo, Angus’s denial, and the things that all four eventually acquire that let them get on with their lives.

Parents, take note: If your wee ones found the frantic rescues and fatherless protagonist of “Finding Nemo” nerve-rattling on first viewing, you will have only yourselves to blame for the teary aftermath of hitching them up to “The Water Horse.” The film’s final half hour contains cliff-hanging perils and spectacles that are intense and noisy enough to rate a cameo appearance by Hollywood audio artists’ great inside joke and arbiter of quality onscreen mayhem, the “Wilhelm scream” (Google it).

If, however, you think they’re ready for a polished and spirited entertainment that gently smuggles in a reminder that wars — even “good” ones — shatter families, and that healing requires the courage to let go of the things that one loves the most, then by all means forge ahead. Better yet, why not let the kids decide? With all the treacly, message-heavy junk they’re likely subjected to, a children’s movie this kid-empowering, wise, tough, and kind shouldn’t be missed on your say-so alone.