CLICKCLICK. Your kids probably won't recognize that sound.
Clicking on an icon selects it, double-clicking opens the file. That relationship has always been dependable; something I've always been able to count on whether I'm using a Mac, a PC or a Linux machine. Select, open. Preview, execute. Highlight, do. But the double-click gesture, which you can still probably hear in your office if you listen closely enough, is on its way out.
Double-clicking is dying.
Do something with your phone. Now watch your thumb. You'll never see a double-tap outside of a game, maybe. Pick up your tablet. Watch your finger. Lots of tapping, none of it grouped. Now, even worse, get your hands on a new MacBook and and look at what's really different about the software. You'll find lots of new gestures, and an iPhone-style app launcher. There's a screen called Mission Control for managing desktops and apps. You can still double-click on the old stuff — the lists of icons in Finder, the app title bars — but there's no double-clicking to be done with the new. Ditto for Windows 8 — Metro is a touch-based mono-tap utopia. Apple and Microsoft, the companies that invented and standardized double-clicking, respectively, are the same ones who are putting it to sleep.
The Apple Lisa was the first computer regular people (well, regular people with 10,000 spare dollars in 1983) could buy that had a graphical user interface. The interface, though, wasn't fully Apple's. It wasn't until Steve Jobs visited Xerox's campus in 1979 that he was fully sold on the GUI concept; so sold that he and his team borrowed liberally from the Xerox Alto, a personal computer that never quite made it to market, in designing their first GUI.
One feature they could definitely take credit for, though, was the double-click. Xerox didn't come up with that; Apple designer Bill Atkinson did.
Atkinson took Polaroid photos to document milestones in the Lisa development process, many of which have been collected by his cohort, Andy Hertzfeld. One bears a note about "double clicking" on a tab to close it; this may be the first known documentation of the behavior.