Dustin Hoffman in Mr. Magorium's Wonder Emporium Courtesy of Fox Walden

When Premiere visits on day 23 of shooting, Hoffman is as kinetic as the shop. Dressed in a spanking vanilla-colored suit with polka-dot suspenders and square-toed shoes, his hair is a mile high. (He worked closely with costume designer Christopher Hargadon to get "a fresh look to appeal to kids, not be some old guy running a store," Hargadon says.) Though the scene is taxing — Magorium has to serve drinks, throw a ball for Mortimer, and change into pajamas, all while spouting tricky dialogue — Hoffman never stops chatting. He suggests blocking moves ("I could back up here if you want me to"), solicits restaurant recommendations ("Not the fancy places, the places where people who know, go"), yaks it up with the crew ("See this bust of Mark Twain? That's what my mother looked like before her nose job"), and mercilessly needles Portman about her boyfriend, Gael García Bernal. "Natalie, one question," Hoffman says earnestly, as if talking about the scene. "What does Gael have that I don't?" She just grins at him and shakes her head.

Mr. Magorium's Wonder Emporium was the first screenplay Helm wrote — he originally sold it to Fox 2000, where it languished for years until he earned enough money to buy it back — and it was drawn from his somewhat solitary childhood. There was a lot of reading, "everything from picture books to Roald Dahl to Truman Capote stories about holidays," and a lot of daydreaming over a vintage Barnum & Bailey poster, the first purchase Helm made with his allowance. "It had all these cool, strange things in there, and the idea that it was from another time and place meant everything to me," says Helm, 32, a tall, baby-faced brunette with thick black bands tattooed around his wrists. While at DePaul University in Chicago, he worked at a "fun and energetic" toy store, and one slow Sunday jotted down a short story that would become this script.

"It's really a collection of the things I loved when I was a kid, and the things that make me feel kidlike now," he says. "It's silly and sweet and heartfelt. As soon as we establish the premise that anything can happen, anything does happen. The only time I get stressed out is when I think, this movie is so weird, people are going to be asking me for years, 'What were you thinking?'"

In keeping with the idiosyncratic mix of eras, colors, and textures in the store, Helm is employing a variety of techniques to convey the magic: "There's vaudeville tricks, tricks we took from magic, theatre, pantomime, puppetry, animatronics, special effects, all the way up to CGI," he says. "We try to do it as thoughtfully as we can, so your average kid won't know if we did it in the real space. So that sense of wonder is elevated."

At one point, Eric has to jump to get a hat down from a high shelf. "We debated about this forever," Helm says. "The initial reaction was, put him on a wire and then remove it in CGI. I said, 'Won't it look like he's yanked?'" Instead, Helm and his fiancée, the actress Kylie Sanchez, visited a circus school in Toronto. "The next day I said, 'We're going to launch him on a trampoline,'" Helm says. "They thought I'd lost my mind. It was one of the first things we shot, the first day, the first take. It looks fantastic. Based on that, I made a bunch of decisions to do as much as we could on camera.

"That effervescence keeps things alive, because all the departments have to work together. I'm asking people to turn back the clock and recalibrate how they do things. To say, 'No, we're not going to take care of it in post, we're going to do it today.' We had people hidden around every corner and behind every lamp. We had doubles to replicate body parts, so it would seem like somebody's arm was extending much further. Once it starts to work, people are excited. You're creating an event and capturing it on film, rather than building something later on. It's way more fun. Way more fun."