You can tell a lot by where the Dardenne brothers choose to put their camera. In their latest film, “The Kid With a Bike,’’ it is mostly fixed in place, eschewing the Dardennes’ preferred brand of wobbly camerawork. “Our characters are the result of an idea, an obsession,’’ Luc Dardenne observed recently. “And this obsession is always in juxtaposition with a moral question, like, in order to have this, am I going to have to kill someone?’’