Ratings, or, What will we tell the children?

From the Times' review of Wendy and Lucy:

“Wendy and Lucy” is rated R (Under 17 requires accompanying parent or adult guardian). It has some swearing, a little drug use and a brief implication of violence, but no nudity, sex or murder. The rating seems to reflect, above all, an impulse to protect children from learning that people are lonely and that life can be hard.