Kids updated my Wii!!!

It will function, just some of the apps wont work.
Thanks, Alex.
I recommend telling off your kids and taking the downgrade off the disc.

Don't panic.

The disk probably loaded a driver for the Wii Motion Plus that is all.

To avoid this in the future install Preloader and enable the option "Skip disc update check" under hacks.

Also make sure you load Bootmii and do a backup. It is a life saver! If you had Bootmii installed you could just do a restore and any changes would have been replaced.