First off, take a deep breath, it's still on your computer, it's just set up for automatic hiding. Probably, your son's also moved it from the bottom to the left or right side too. All easily fixed, and once you know the trick, you can easily change and tweak it to your heart's content too. Then you'll apparently need to get back at him for his mischief!

The Dock is designed to either be always visible (which makes it like the Windows Taskbar along the bottom of those systems) or to hide until the cursor is along the very edge of the screen, at which point it magically appears until you move the cursor back to the middle area of the screen. Personally, I like the "auto-hide" feature because it removes some clutter that would otherwise distract me when working, but a lot of people set the Dock to be very small but always displayed along the bottom or right side.

Since you aren't sure where it is, you could just move your cursor to the left edge, right edge and bottom edge to see which causes it to show up, but there's an easier way, off the Apple menu:

The "Hiding" feature is what's made your Dock "disappear" so simply select it to reenable it and you'll be surprised what pops up (and probably where it pops up!). Magnification means that the icon that the cursor's over is larger than those adjacent, something that's a very handy feature if you make the Dock really tiny.

Notice that the Dock can also be moved left, right or on the bottom. Most people I've seen have it on the bottom, but the right side can be a good place for it too, depending on your preferences.

We're not done yet, though. Choose "Dock Preferences..." and here's what else you can tweak:

Here's where you can easily change the size of the Dock with the slider, along with the percentage of magnification if you opt for that effect.

If you're on a slower Mac, you might decide to turn off some of the visual effects, but otherwise the options are self-explanatory. Experiment, see which you prefer!

Finally, if you have a folder on the Dock itself, right click on it and there are yet more options for how things behave:

I'm a fan of the "Grid" layout for folder contents, personally, but again, experiment and see what you prefer. And as you can see, adding the "Applications" folder to your Dock (which you can do by just dragging it from the Finder window onto the Dock) is a big win and - in my opinion - alleviates the need to have tons of icons on the Dock in the first place.