iMac wont stop talking to me!

Open Universal Access preferences and turn off VoiceOver.

The System Preferences section has controls for a variety
of things, one of them to look into and check settings is of
the name, "Universal Access" to see if the defaults (off)
have been turned on in any of these optional controls to
have the computer talk, show text large, reverse desktop
from white on black to black on white; and other settings.

If you allow kids to have access to your main or Admin
account, then expect all things inside the computer to be
available to them. Your work will be cut out for you when
you'd have to look in there again for the next odd thing.

Setting up a second or third user account will less access
permissions and limited use of applications, no access to
change system level settings, and other stuff is a part of
the Mac OS X; and new users can be carefully limited.

{I'd have posted earlier, but I had to check to make sure
and offer other suggestions, since you have kids there.}

Good luck & happy computing! 🙂

PS: do you have kin? Perhaps iCurly, iLarry? 😉

iMoe --
You've got all the right answers here.
Your kids probably did it by pressing the Command and the F5 key at the same time.
🙂