LOS ANGELES — Given its premise, “Alexander and the Terrible, Horrible, No Good, Very Bad Day” could have been a lot more horrible and no good than it is.

In fact, at a quick 82 minutes, this straight-arrow family comedy about a day when misfortune comes to visit and stays awhile goes down relatively painlessly.

Thirty-two-page children’s books aren’t the easiest properties to adapt into feature-length scripts, which may be why it took 42 years for someone to figure out how to handle Judith Viorst’s perennial.

Screenwriter Rob Lieber’s way of filling out the conceit to feature-length running time is to have atrocious things happen not only to the 11-year-old title character but to his entire family and spread the calamities across two days.

“The day before” the big day in question, the agreeable Alexander (Ed Oxenbould) receives a mighty blow upon learning the most popular kid in school is throwing a party the next night at the same time as his own 12th birthday party, meaning that no one, including the girl he likes, will come to his bash.

Also on tap the next day: His unemployed dad Ben (Steve Carell) has a big job interview with a video gaming company, mom Kelly (Jennifer Garner) is overseeing a celebrity book reading event for her hard-to-please boss, brother Anthony (Dylan Minnette) is chauffeuring snooty girlfriend Celia (Bella Thorne) to the junior prom provided he passes his driver’s test and sister Emily (Kerris Dorsey) is starring in a production of “Peter Pan.”

The worst day begins with everyone waking up late. Alexander is the recipient of the only good news: The popular kid has chicken pox, so Alexander’s bash is back on full steam. Otherwise, Murphy’s Law lays siege to the family.

The arguable comic highlight is Anthony’s driving test, which is presided over by a farcically overbearing woman (Jennifer Coolidge). Kelly’s mishaps with her author’s event simply seem too preposterous to be funny.

On the other hand, the interplay between Ben and the gamer geeks is not unamusing, even if Ben’s tolerance for agreeably filling the role of a “fommy” (father-mommy) would seem to exceed ordinary limits. The homily-laden wrap-up is enough to make you hold your nose, but it only lasts a moment.

The cast is uniformly game and the filmmakers have thoughtfully included something at the end for all the moms who will drag the small fry to see this — a bunch of hunky Aussie cowboy strippers who begin performing before they realize they’re at a child’s birthday party.