There’s an existential question at the heart of writer/director John Krasinski’s new kid-friendly semi-animated movie “IF.” It’s a simple query, but it speaks to the limitless potential of a child’s imagination, and it gets asked again and again: “what if?”

“IF” is also an acronym in the film for “imaginary friend,” and so the question is asking, “what imaginary friend?” But it’s also spurring the audience to consider the possibilities that seem impossible, like if our imaginary friends never disappear with time and memory, but remain in the world, purposeless and friendless.

It’s an interesting premise, and Krasinski has leveraged his hefty Hollywood contacts list to contribute voices to the imaginary friends. However, a cute premise and a bunch of stars are pretty much the only things going for “IF,” which is a surprisingly somber film with serious storytelling problems, because writer Krasinski didn’t bother to flesh out the fantastical world-building.

It’s a bit ironic because the characters repeatedly talk about the importance of stories. In an opening narration, our heroine Bea (Cailey Fleming) describes how when she was a child, her mother would ask for a story, and later, she tells a story to her father (Krasinski) in one of the film’s climactic, cathartic moments. Krasinski insists that stories are important, but never actually demonstrates why or how. And on a structural level, the storytelling of “IF” itself is a mess, a heartfelt but dramatically inert endeavor that whipsaws between tones ranging from whimsical to morose.

This may be a film about imaginary friends, but what it’s actually about is dead and dying parents. The “Ifs” are the coping mechanism, and they are also the emotional tether to childlike wonder and comfort in escapism, which is something that 12-year-old Bea needs more than ever. In an opening montage, we see her happy childhood, and her mother (Catharine Daddario) slipping away due to illness. When we meet Bea again in the present, her father is in the hospital with a “broken heart” (though he’s plenty spry enough to pull childish pranks and hijinks).

Bea is staying with her grandmother (Fiona Shaw) in her childhood apartment in Brooklyn Heights, strangely left to her own devices, and ends up falling in with her reticent neighbor Cal (Ryan Reynolds) and his two magical associates, a giant purple guy named Blue (voiced Steve Carell) and a ballerina Minnie Mouse creature, Blossom (voiced by Phoebe Waller-Bridge).

Blue and Blossom are Ifs whose kids have grown up, and they’d like to find new ones to befriend. After they explain their plight, Bea takes on the matchmaking task as her new “job.” It’s never explained what will happen to the Ifs if they don’t get paired up, as it seems they just go live in a retirement home underneath Coney Island. But Bea seals the deal with a musical performance of Tina Turner’s “You Better Be Good to Me,” which is both a callback to her own childhood memories but also feels like an extensive inside joke.

They soon realize that they need to be tracking down the adult pals of the Ifs instead of looking for new ones, and so Bea roams New York City with Cal, Blue and Blossom looking for these kids and trying to activate their sense memories so that they can see their If again.

There’s a lot of potential disbelief to suspend here, and an audience that would be willing to go to these places, if there was a story structure in place, a set of rules and regulations about these imaginary creatures. Who can see them? Why does her grandmother not wonder why Bea is running off to Coney Island all day? Is her dad in a mental hospital? Is any of this actually happening?

The good news is that the film looks great, with rich, vintage production design by Jess Gonchor, and it’s beautifully shot by master cinematographer Janusz Kaminski. But the whole conceit is so undercooked it could give you salmonella./Tribune News Service

“IF”

Rated PG. At the AMC Boston Common, South Bay Center, Causeway, Alamo Drafthouse Seaport, Landmark Kendall Square Cinema and suburban theaters.

Grace: C