WE WERE BACK in Chicago for the holidays last year, and one miserably snowy day my five-year-old and I finally found something to do. Bowing to the boy's excited wheedling, I grudgingly agreed to crawl (as one must) deep into my parents' crawlspace to unearth all the Lego sets I'd secreted away upon puberty some 20 years ago.

He was transfixed! And I loved watching him play with the very same pieces my own fingers had deftly assembled and disassembled when I wasn't much older. But I also felt nervous, jealous—especially when he started handling some of the sets I'd built from scratch.

The feeling was ugly, like he wasn't my kid but just some kid. Who was totally going to break my stuff. These Legos, it turned out, were still mine. And I had to let them go.

That rite of passage was all I could think about, weeks later, after leaving Warner Bros.' should-be-shitty-but-isn't The Lego Movie—the latest low-concept gem from directors Chris Miller and Phil Lord (Cloudy with a Chance of Meatballs, 21 Jump Street).

The story seems obvious: A hapless chosen one—an ordinary minifigure named Emmet (Chris Pratt)—is called by destiny to save creation from the villainous, fastidious President Business (Will Ferrell) and his chaos-ending Krazy Glue.

Of course Emmet prevails—after a wild ramble, all full of gags and nerd references, that pokes fun at Lego's crossover-laden past.

But instead of plodding through like one more cynical big-screen commercial (hi, Transformers!), The Lego Movie manages to weave an enlivening magic spell of nostalgia that's equal parts hysterical, subversive, beautiful, and sweet.

And the lesson is that Legos—like so many things in life—lose their joy when you stop building and playing, and start treating them like dusty museum pieces instead.