My five- and seven-year-old constantly fight over who gets the iPad first. We have one, and they get to use it in tiny doses, usually when I'm at my wit's end. Their favorite app? ScratchJr, MIT's ...

A lone starfighter floated on a pitch black computer screen, rotating on an invisible axis. All at once, the ship lurched into action, firing a white bolt that dissolved its target, then swiveled to ...