Saying that film's make children do drugs is the same as saying video games make us more violent. If a video game or a film influences you into drugs or violence, you must already have had thoughts about doing them anyways.
Also, usually films with drug content and the like have higher ratings, usually 18's so kid's shouldn't be watching them anyway. Wanna blame anyone? Blame the person who rolls it up and then lights it or injects it or whatever.