Trolls starts as it means to go on: with a big pink, sticky splat of bubble-gum, as the collective voice cast – led by Anna Kendrick at her sunniest – cover Junior Senior's Move Your Feet. There is a case to be made against Trolls, a musical-comedy that manages to turn The Sound of Silence into a perky singalong anthem, and that primarily exists to shift weirdly hirsute dolls.

A lot of care goes into that textured, lustrous Day-Glo hair. A lot less attention has been lavished on the plot, but here goes. An overture introduces us to the tyrannically happy trolls who, we are told, are consumed by a race of ogres known as Bergens at an annual festival.

In order to keep the rating suitable for the very young target demographic, the trolls escape their larger captors before any onscreen cannibalism can occur. They set up home in a retina-dazzling part of the forest, where they are free to sing, dance, hug every half-hour, and, in the case of Princess Poppy (Anna Kendrick), make adorable felt scrapbooks.

Eventually, their exuberance brings them, once again, to the attention of the Bergens, prompting Poppy to call upon Branch (Justin Timberlake) – the sole grumpy troll – to aid her in a rescue mission.

This slender narrative is padded out by karaoke tunes, many of which were hits before the parents of the target demographic were born: Earth, Wind & Fire's September gets what may be its millionth movie airing. The original tracks (bar Timberlake's Can't Stop the Feeling and the Let-It-Go-alike Get Back Up Again) aren't necessarily as memorable as the covers of Lionel Richie's Hello or Gorillaz' Clint Eastwood.

One troll appears to urinate glitter and another poops cupcakes but the film is still a good deal less scatological than the similarly-minded Alvin and the Chipmunks, and a good deal more charming than either of the Smurfs movies. Kendrick and Timberlake bring snappy comic timing, even when the dialogue could be wittier. Co-director Walt Dohrn steals the picture as a high-fiving cloud-bro.