Error message "iPod is disabled. Try again in 22,236,924 minutes." I think my son was trying to guess the passcode! What do I do?

I can't wait 42 years!
No harm done, that is if you have a backup on iTunes.
The Apple Support pages tell you can reset the block by restoring it within iTunes. 


  If you cannot remember the passcode, you will need to restore your
  device using the computer with which you last synced it. This allows
  you to reset your passcode and resync the data from the device (or
  restore from a backup). If you restore on a different computer that
  was never synced with the device, you will be able to unlock the
  device for use and remove the passcode, but your data will not be
  present. Refer to Updating and restoring iPhone, iPad and iPod touch
  software.