The fact that it wasn’t pre-screened for critics might make you expect the worst of this kidflick, but “Aliens in the Attic” isn’t all that bad. In fact, if it were being shown on one of the family cable networks, it would be something adolescent boys in particular would enjoy. It’s out of place on the big screen, though, except for the most undemanding audiences.

The title pretty much says it all. The Pearson family—Stuart (Kevin Nealon), Nina (Gillian Vigman), their children Bethany (Ashley Tisdale), Tom (Carter Jenkins) and Hannah (Ashley Boettcher)—along with Stuart’s brother Nathan (Andy Richter) and his sons Jake (Austin Butler) and twins Art and Lee (Henri and Regan Young) and the kids’ grandma (Doris Roberts)—are vacationing at a Michigan lake house. (Curious geographic note: they’re shown leaving Chicago and arriving at their destination after a brief road trip, which suggests the makers didn’t look very closely at a map.) The place is invaded by four little creatures from the planet Zircon with a mission to recover a device buried under the house that will initiate an invasion of earth. And since the critters have a lobotomizing gun that can turn adults into helpless automatons—a fate that befalls not only granny but Ricky (Robert Hoffman), Bethany’s smarmy college boyfriend—it’s up to the kids to defeat them and save not only their family but the world.

I suspect it will come as no surprise that they do.

Much of the picture is devoted to slapstick battles between the CGI creatures (voiced by Thomas Haden Church, Josh Peck, Ashley Peldon and Kari Wahlgren) and the children, but time’s taken out for some heart-to-hearts between Tom, a smart kid who’s tanking his classes in order not to be thought a nerd (the experience with the aliens makes himself understand the value of knowledge, of course), and his dad, and even more violent action involving Ricky, who’s turned into a sort of crazy elastic man under alien control, and grandma (a big martial-arts fight between the two after the kids get granny’s control device is supposed to be the piece de resistance, but is taken too far). The big twist—though it’s hardly a surprise—is that one of the scouting party turns out to be nice and becomes the kids’ ally. And at the end there’s a “Power Rangers” moment when two of the critters grow to gigantic size and face off against each other.

The effects in “Aliens in the Attic” look pretty ordinary in this day and age, but they’d certainly pass muster on the small screen. It’s unfortunate that the “good” alien so closely resembles E.T. (adding an extra pair of arms isn’t really much of a disguise), and that his final goodbye is so closely modeled on Spielberg’s film (John Debney’s music even recalls John Williams’ at that point). But the youngsters are an appealing bunch, though Boettcher should have been reined in by director John Schultz a bit—her mugging is right out of a bad sitcom—and Tisdale comes off rather shrill. The adults are another matter. Nealon, as usual, italicizes every line, Richter’s doofus routine gets old fast, and Tim Meadows’ turn as the local sheriff is so laid-back it might have been phoned in. Roberts, looking very frail, doesn’t have the comic timing she once did (and should have been spared a gag about her dentures), while Hoffman—or his CGI double—chews the scenery, which is what he’s expected to do, and kids will love his “stuntwork.”

There’s some of the same sort of simple highjinks here found in such earlier kidflicks like “Sky High” and “How to Eat Fried Worms,” and the picture doesn’t descend to the level of stuff like the “Spy Kids” movies. But it lacks magic, and except as a harmless diversion for the youngsters in a rainy afternoon, you can safely hold off until it shows up on DVD.