I'm glad that your grandchild/child/niece/nephew/godchild has shown an interest in music, and you've decided to teach them yourself to "save some money."
My issue is, when I show you a beginning level book for that instrument in his/her age level, because you asked what book to use, and you don't even understand the first lesson, maybe you shouldn't be the one teaching said child!
Pay for the lessons!
End of rant.
*I would say this about teaching any subject!