A delicate balance of sweetness and absurdity marks this British comedy by Garth Jennings (The Hitchhiker's Guide to the Galaxy), about lonely schoolmates who forge an unlikely friendship as they collaborate on a video sequel to the brutal Sylvester Stallone flick First Blood. Directing the project is a rebellious bully (Will Poulter) who's been abandoned by his rich father to the care of a neglectful older brother; his Rambo is a meek artist (Bill Milner) whose widowed mother is raising him under the strict doctrine of a pacifist Christian sect. Jennings's film, with its missing fathers, sometimes threatens to become cloying, but it's almost always righted by a healthy dose of slapstick or the spectacle of little kids posing as muscle-bound killers. This is stupidly rated PG-13 for “some violence and reckless behavior,” but I can't imagine a better movie for children and adults to enjoy together. 96 min.