If memory serves, the last cinematic franchise to go 3-D the third time around was “Jaws” in 1983. The result was not exactly spectacular: the picture looked dark and murky, and the technical problems didn’t help a decidedly silly plot. The movie was a deserved bomb, and should have brought the series to a halt. (Four years later “Jaws: The Revenge” buried it.) “Spy Kids 3-D: Game Over” will probably be much more successful, because the target audience of pre-teens is likely to be more tolerant of the visual flaws, which remain serious–this 3-D system isn’t anywhere near the quality of the IMAX version that audiences have come to expect as the top of the line, with images as fuzzy and indistinct as those older viewers will recall from years long gone by.

That’s one of the reasons why this is easily the weakest installment in the popular kids’ series, and one can only hope that the subtitle is more than just a reference to the virtual reality game at the center of the very thin plot. That game, we’re told, has been invented by a not-so-mysterious villain called The Toymaker (Sylvester Stallone) as a means of brainwashing its eager young users and thereby remolding the world. The younger of the Cortez children, Juni (Daryl Sabara) has left the spy service and become a private eye, but he reluctantly rejoins the government agency in order to enter the game and rescue his sister Carmen (Alexa Vega), who’d been sent to unplug the thing and gotten trapped inside. The rest of the decidedly episodic picture has Juni, joined by some other players, a liberated Carmen and their grandfather (Ricardo Montalbon), who’s freed from his wheelchair in the virtual environment, attempting to bypass all the obstacles and reach the game’s final level. Complications arise when it’s revealed that the Toymaker was responsible for the accident that left Grandpa disabled.

“Game Over” is, of course, a message movie–it preaches the power of family (though in this case a highly extended family, since it’s supposed to include everybody–it doesn’t take a village, apparently, but the whole world) and the importance of forgiveness as means of resolving problems. But tykes probably won’t care about all that as much as they’ll dig the video game-inspired action sequences, which include “Tron”-like races and robotic fistfights. Even though all the effects are decidedly cheesy and the 3-D photography mutes the color and excitement, kids will probably take to the mindless, and largely benign, violence and appreciate the continuous, if largely arbitrary, stream of stuff that seem to pour out of the screen toward the audience. Some of the effects don’t really go much beyond the pointless swinging to and fro that John Candy used to indulge in as part of the 3-D parody sketches on the old SCTV series, but they may seem cool to youngsters to whom it’s a novel experience. Nonetheless honesty demands that one admit that the level of invention on display here–both narrative and visual–is hardly an advance on live-action kiddie TV.

The acting’s about on that standard, too. Sabara and Vega continue to perform like pleasant-faced amateurs–a fact particularly lamentable in Sabara’s case, since he has so much screen time in this installment. The other youngsters in the cast are actually a bit better, though not by much. The adults, moreover, mug and froth as though they were playing to an audience of imbeciles. Stallone does four characters–or, more properly, four parts of a single character–and manages to be bad in each of them. Montalban presents himself as an icon in every respect; it’s only at the close, when he permits himself a snide reference to Corinthian leather, that he manages to bring much life to the party. There are scads of cameos–virtually every character from the first two films (including Mom and Dad, played by Carla Gugino and Antonio Banderas) appears briefly in the final scenes, and a few new ones are added earlier–but they add little to the fun beyond the momentary shock of recognition.

Once again you have to give Austin-based auteur Robert Rodriguez credit for performing what amounts to a one-man show behind the camera. He wrote the picture, directed it, edited it, shot it, composed the score, designed the production and supervised the effects. What he hasn’t done, unfortunately, is make a movie that will endure the way the best children’s films do. “Spy Kids 3-D,” like the previous episodes in the series, is the sort of thing kids will enthusiastically embrace for a while and then toss aside. It’s the Pac-Man of movies, and Rodriguez would be smart to end the series before the tykes move on to the next flavor of the month.