Most modern consoles offer the ability to restrict kids to only playing games of a certain rating or for a given length of time, but parents often don't know how to set them up. A series of videos from the Interactive Games and Entertainment Association shows how to do that.
You can see the guide for the PS3 above, and there are also videos for Xbox, Wii and PCs on the IGEA YouTube channel. None of this is likely to be news to Lifehacker readers, but they're a useful resource to point to for confused relatives.
They're also timely in light of the current push to introduce an R18+ rating for games, an issue which Mark over at Kotaku has covered so thoroughly that we have literally nothing to add.