They took two ordinary-looking kids and gave them super powers. No they didn't, you say? Well, in the first minutes of the film, the kids go to work out in their own private gym. Suddenly these ordinary kids are leaping and flipping about as if they have donned jet-packs. Their leaping and flipping is accompanied by the obligatory swishing and zooming sound effects. Ick.
What should have been a film about a couple of ordinary homely kids working hard and using their guts and determination to save their beautiful, talented spy-parents turns into a contrived special effects extravaganza. We're supposed to suspend belief and buy that these two kids can do extraordinary physical feats just because their parents are spies?
Subtleties are so often lost on Hollywood. There are so many movies that do it better. If you want to see kids use their guts and courage to survive adversity (without obvious special effects) try Adventures in Babysitting. Even Home Alone is more believable than the Spy Kids drivel.