Music Theory – wanted to read post

Oh no!!   —  I noticed that a thread had been started about music theory.  I was so wanting to read it and glean some good info/ideas.  The last few days have been busy, so I’ve been waiting until I had a few minutes to spare and could sit and read all the responses.  Now I finally have that time . . . and the post must’ve been lost in the technical difficulties that Doug posted about.      So, if it isn’t too much to ask, anyone who would re-post about any music theory that they have used and enjoy.  My kiddos are 6 and 8.  I was wanting to start them on piano this next year, but we are not moving back by Grandma and Grandpa (who have the piano!), so I’m not so sure that will work out.  We will probably start some guitar.  I thought some music theory would be good so that when we do get a chance to start some more formal music lessons, they will already have an understanding of music theory.    Thanks!