There are some interesting familial themes lurking under the scary-movie surface of Steven C. Miller’s horror flick, but they’re only tantalizingly suggested, never explored. Instead “Under the Bed” devolves into a standard-issue creepshow, undermined by script holes and a meager budget that brings distinctly subpar effects.

It does, however, boast two attractive young leads in Jonny Weston and Gattlin Griffith, who play brothers Neal and Paul Hausman. Neal, the older, has been away for a couple of years, living with an aunt after a house fire in which his mother died, although the scuttlebutt among local kids is that he’s been in a mental institution and was probably responsible for the deadly blaze. Adolescent Paul has stayed at home, but his constant nightmares have unnerved their volatile father Terry (Peter Holden), who’s liable to rages whenever his sons don’t seem able to act normally, though their stepmother Angela (Musetta Vander) is more understanding.

It’s quickly revealed that the reason behind the brothers’ emotional turmoil is that a monster lives beneath Paul’s bed, terrorizing the boys—and their mother died trying to protect them from it. In a more intriguing film, the creature might have portrayed as some sort of emanation of their psyches—like the destructive being of “Forbidden Planet”—but in the pedestrian script by Eric Stolze, it’s just a boogeyman that, it’s suggested, feeds off the dead skin people shed each day. The boys do battle with it, and their parents—along with a neighboring family consisting of a doofus dad (Bryan Rasmussen), his nice daughter Cara (Kalcie Stranahan) and his two obnoxious sons (Tyler Steelman and Sam Kindseth) get sucked into the fight; some survive and others don’t. Eventually Neal follows Paul to an alternate reality to save him after he’s been taken there by the beast, and defeats the critter with some unexpected help from what’s left of his dead mother.

The best part of “Under the Bed” is the relationship between the two brothers, which Weston and Griffith play nicely. By contrast all the adults come across as an incredible bunch, and both Holden and Vander overdo things (though their parts are so poorly written that it would have been hard for Laurence Olivier and Meryl Streep to do much with them). And the effects are of the bargain-basement variety, with lots of smoke and a rubbery monster played by Ivan Djurovic. Miller should have given some zip to the effects-heavy sequences, but instead he handles them flatly, and his lethargic editing adds to the problem. Ryan Dodson’s overemphatic, overloud score doesn’t help either.

The result is a picture that feels like an extended, slightly more jazzed-up episode of a cable TV show like “Goosebumps” or “The Haunting Hour.” Adolescents who go in for such stuff might find it amusing without being much frightened by it, but it’s too tame and plodding for anybody else.