My Babysitter's a Vampire (2010)

No parents. No rules. No pulse.

Geeky 14-year old Ethan is left to babysit his younger sister, Jane, with his best friend Benny but after Ethan inadvertently puts Jane in harm's way, his parents hire a professional babysitter, the beautiful yet mysterious 17-year-old Sarah who, unbeknownst to them, is actually a fledgling vampire.