If you aren't a touch-typist, you may have to keep it up for a while. Your grandchildren are right, though. It's better for your wrists if the keyboard is flat or even angled slightly downward. This puts the wrists in a more neutral position and takes the pressure off the carpal tunnel.

Try to lower the board once you learn the keyboard and can type without looking. You may want to do this gradually if there are several positions possible. That way the change in tension on your wrists and hands won't be as much as if you did it all at once.