Sort of a tangent, I was visiting a friend with a young daughter. After seeing how she acts when watching a movie, and how she reacted when it was time to stop, I wouldn't let my (hypothetical) children be exposed to video, or really the Internet at all, until they were at least teenagers.
I know, I would have to go live with the Amish or something, but daaaaamn... TV and Saturday morning cartoons were bad enough ~30-40 years ago. We're warping kids' minds.