So you’ve got tween sitcom princess Victoria Justice in your movie. You’ve got trailers that give off an “Adventures in Babysitting” vibe, complete with (OMG, so annoying!) an Underoos-clad kid as Justice’s Halloween mischief-making little brother. You air those trailers on synergistically connected Nickelodeon, sandwiched between promos for Justice’s “Victorious” and commercials for the Dora & Me Dollhouse. You cutely title the whole enterprise “Fun Size.” And then? Well, naturally, you drop a fried chicken joint’s giant mascot statue on top of your characters’ teenmobile, and let the big bird start humping away.

While its story line is straightforward enough, this PG-13 debut feature from “Gossip Girl” co-creator Josh Schwartz is all over the map in the details it throws at us, and the level of immaturity it aims for. Justice plays Wren, a dorky but clearly fabulous high school senior who gets a very pointed Halloween party invite from the class hunk, only to learn that she’s got to take her odd-duck brother, Albert (Jackson Nicoll), trick-or-treating. Seems that Mom (Chelsea Handler, go figure) has gone a little wacky since Dad died — back story that’s alternately semi-poignant and ignored — and plans on partying with her studmuffin boyfriend. Wren does what she must, but when she gets separated from Albert after just a few stops, her night really gets a shakeup.