The easy things first: The marketing people charged with finding audiences and customers for movies, recorded music and video games need to be told -- clearly -- by top management that media and marketing plans must respect the content ratings. There should be no treating teens or subteens as desired customers for age-restricted products, and there should be more attention paid to careful selection of media venues (and more attention paid by media owners to where and when they accept ads for products that come with advisories).
Retailers and theater owners need to do the obvious, and many already are: Treat the ratings seriously and act to stop, to the extent possible, the sale of age-restricted tickets and products to kids too young to buy them without a parental OK.
What media should or should not be used because some number of kids are in the audience will be complicated to decide. There may be no one answer. The FTC suggests 20% of under-17s in the audience is "substantial." There will be other views. One thing is clear. Self-regulation is the quickest route to action, and industrywide self-regulation creates a level playing field. Now the entertainment industry needs to show it believes in its own ratings and is willing to market accordingly.