A funny and charming romantic comedy, 13 Going On 30 is a gender-tweaked take on Tom Hanks' child-in-adult-body hit Big. When her 13th birthday party goes pear-shaped, Jenna Rink (Christa B Allen) wishes she was 30. And, with a sprinkling of movie magic, she wakes up as a glam, 30-year-old magazine editor in Manhattan, played by Jennifer Garner. Predictable, easygoing laughs ensue, as she tracks down old school friend Matt (Mark Ruffalo) and realises what an immoral schemer she's become.

The child inside body-swap concept isn't original, but as proved by the Freaky Friday remake, it is durable: perhaps because it allows adults to recall the embarrassment and enjoyment of their early years, while children can dream of instantly embracing the "grown-up" world.

"A LITTLE INNOCENCE GOES A LONG WAY"

If you start thinking about it, the ethical issues raised by a 13-year-old girl in an adult body, falling for the 30-year-old incarnation of her teenage best friend, could prove a headache. But 13 Going On 30 is a fairytale which, while not blind to sex, mimics its lead's naivety and trusts the audience not to ask difficult, killjoy questions. It's about maintaining, or regaining, an attitude of child-like enthusiasm and openness. For a back-biting material girl, it argues, a little innocence goes a long way.

The moral is writ large in Jenna's cuddly, retro redesign plans for her magazine - a concept the filmmakers can't have been entirely convinced by, or they'd have made it look more appealing. It's here that Gary Winick's sprightly caper becomes a little stodgy, but Garner carries it through with a performance of bubble, fizz and glee. Is she a great actress? We'll see. She's certainly a star.