A single man, in love with a single mom, wants to take their relationship further, and wants to be on good terms with her kids. The relationship is complicated by the fact that he leads a sort of double life, part of which he can't tell her about. Soon, the family becomes entangled in his alter-ego role, misunderstandings threaten the relationships, and the hero's two lives have to be sorted out. No, this isn't The Spy Next Door, but even my 10 year old was struck by the parallels.
Despite the similarities, The Tooth Fairy does stand on its own. The Rock, now known as Dwayne Johnson, stars as Derek Thompson, a pro hockey player past his glory days. He's still known as The Tooth, due to his proclivity for knocking out the teeth of his opponents. After he nearly reveals to his girlfriend's daughter that there's no such thing as the tooth fairy, he's sentenced to serve as a tooth fairy. He's taken to the magical tooth fairy headquarters where Julie Andrews is the head tooth fairy, and Billy Crystal is the gadget guy, supplying the shrinking cream, invisibility spray, and the cat horn. (By the way, when Crystal's character was introduced, I thought, "That guy is trying to act like Billy Crystal." But he looked only vaguely like Crystal. Sure enough, it's him.)