Since I've been encouraging my grandchildren to study and memorize the articles of faith with me this year, I searched for a tool to help with that process. Bingo! Zack & Zoey Explore the Articles of Faith (DVD/CD) is great. Sammy and Quinn reported it a winner. They were singing some of them in no time.
"I have commanded you to bring up your children in blight and truth." Doctrine and Covenants 93:40
I believe this applies to grandparents teaching grandchildren if their parents allow it.