How to lock the keyboard - macbook

I know most people are trying to UNlock their keyboards.... 🙂
My wife uses her macbook to show movies to my 3 and 4yr old while traveling. But the kids can't helpthemselves and after 5 minutes try and "type like mama". which inevitably stops the DVD causes another program to open or something. Anyone with kids knows this instant "mayhem and change" on the screen only encourages the behavior.
Good kids.. but who can resist playing with a Mac, regardless of how old they are 😉

Is there a way to lock the keyboard to that only pressing a certain combo will enable it again? (and keep programs/DVD running)

Thanks
-mosermac2