A 13-year-old girl wishes she could be “30 and flirty and thriving” and wakes up the next day in the sleek body of Jennifer Garner (the star of TV’s spy drama Alias). This new movie, of course, is just a gender-switched version of the old movie Big, which brought Tom Hanks his first Oscar nomination. The obvious hope is that this rehash will give a similar lift to Garner, and it just might: Seeing her larking about like a wide-eyed kid is the movie’s chief pleasure, and it’s certainly as far from Alias as she could get. But she does more for director Gary Winick and writers Cathy Yuspa, Josh Goldsmith and Niels Mueller than they do for her. They never go beyond their basic idea, leaving all the entertainment to Garner’s flair for comedy (and, in one scene, her better-than average dancing).