For a movie supposedly designed to disprove an adage spoken by one of its villains–that a spy is only as good as his gadgets–Robert Rodriguez’s sequel to his surprisingly well-received 2001 family film is a flashy but curiously heartless exhibition of technical wizardry, apparently based on the premise that a kidflick can do without much feeling so long as the bells and whistles are in place. “Spy Kids 2: The Island of Lost Dreams” is wildly colorful, crammed with special effects and incessantly busy, but largely devoid of charm. It’s as though Rodriguez were so anxious to prove that his Austin studio could match everything the California SFX shops can do that he’s forgotten that an audience has to be given some reason to care about the characters who interact with the visuals. Some of us were less than enchanted by the first installment anyway, but even those who embraced it enthusiastically may find this one a disappointment in all but the surface sense.

The plot devised by Rodriguez is a very thin reed on which to hang his admittedly impressive (if ever so tacky) visual wares. Carmen and Juni Cortez (Alexa Vega and Daryl Sabara), the pint-sized heroes of the first flick, are now operatives in a junior-league US intelligence service (a notion that, if you stop to think about it, has vaguely fascist overtones). In an operation at a Texas amusement park (whose owner, in a broad cameo, is a drawling Bill Paxton), however, they’re bested by their chief kid rivals, Gary and Gerti Giggles (Matt O’Leary and Emily Osment, Haley Joel’s sister); simultaneously their father Gregorio (Antonio Banderas) is passed over for a promotion in favor of his rival, the Giggles’ dad Donnagon (Mike Judge). Moreover, Juni’s infatuation with the US President’s neglected daughter (Taylor Momsen) and his dislike for Gary lead to the loss of prototype for an instrument that can shut off all power in its vicinity, and the poor kid is relieved of his duties. Gary and Gerti are assigned to track down the source of the lost invention on a secret island in the Bermuda Triangle, but in order to retrieve their reputations Carmen and Juni effectively usurp the task, and before long they find themselves in the domain of a benign but peculiar scientist (Steve Buscemi) who’s created a menagerie of huge, cross-bred monsters. To make matters worse, Gary and Gerti follow them there, with a hidden agenda of their own; and a worried Gregorio and his wife Ingrid (Carla Gugino) follow, accompanied by Ingrid’s parents (Ricardo Montalban and Holland Taylor), who’ve never thought much of Gregorio. Everything comes to a head when Donnagon shows up, too–up to no good.

To be sure, this scenario provides plenty of opportunities for juvenile adventure and Saturday morning TV-style banter, and Rodriguez proves an able effects technician (he also employs high definition video much more effectively than others have done recently). But the director’s visual imagination is less impressive this time around–the surrealistic tone that infused many of the settings in the first installment is mostly lacking here. And despite a frenetic pace and an obvious eagerness to please, “Kids 2” grows increasingly tiresome as it goes along; by the close it’s more exhausting than exhilarating. I have as much admiration for Ray Harryhausen’s classics as anybody, but though the first half-hour of “Kids” is no great shakes, the picture really takes a tumble when Alexa and Juni reach the island and confront the computer-generated beasties that serve as homages to the master’s stop-motion ones. One sequence goes so far as to mimic–poorly–the famous swordfight-with-a-skeleton episode from “The Seventh Voyage of Sinbad,” down to a cheap imitation of Bernard Herrmann’s xylophone-and-woodblock score. Perhaps this segment of the picture would have been more enjoyable if Buscemi weren’t so bland as the resident scientist; he brings nowhere near the style to his part that Alan Cumming and Tony Shalhoub (here reduced to the briefest cameos) did to their roles in the first feature, and as a result he’s more boring than endearing. Even worse, Vega and Sabara exhibit a smug attitude that makes them far less likable than they were in the initial installment. The new kids–O’Leary and Osment–are one-note figures and hardly pick up the slack–a particular disappointment in the case of O’Leary, whom Paxton directed to such fine effect in “Frailty.” As for the returning grownups, Banderas and (especially) Gugino are surprisingly colorless, though Banderas gets to do some (poorly choreographed) slapstick fighting near the close. As if to compensate, Taylor and Montalban overplay broadly; Montalban, incidentally, spends the movie riding about in a flying wheelchair–one trusts that the seat is made of real Corinthian leather.

Rodriguez has now proven that he can replicate, in central Texas and at far reduced cost, much of what the effects wizards in California churn out. Now if only he learned the lesson that’s also eluded his west coast brethren for so long: the SFX have to be in support of a good script, not a replacement for one.