“Ratz” is a clever, entertaining fantasy for the entire family. Vanessa Lengies and Caroline Elliott are charmers as geeky ducklings, who will no doubt soon be lovely swans. They are real teenagers, with the word “like” used to begin nearly every thought. And, of course, each awkward moment they undergo is a major catastrophe that most adolescents will relate to. There are some genuinely funny moments, including seeing the girls trying to manage the rat-boys by constantly feeding them.