Explaining Cassette Tapes to my 6 year old...

Me:  Singing along to a 70's song on the radio.
Keira:  Mom, how do you know that song?
M:  My Dad used to listen to it when I was growing up.
K:  Did he have it on his iPod?
M:  There were no iPod's then.
K:  Oh, just iPhones.
M:  (Laughs) No, we didn't have those either.
K:  (Astonished)  What did you have?
M:  We had radios, like the one in our garage, and our music was on cassette tapes.
K:  What's a cassette tape?
M:  You know that white rectangle with the cord on it that we use to plug our iPods into the van?  That's a cassette tape.
K:  Oh, I'm sure glad that we have iPods now when I'm growing up.
M:  Me too, Keira!  Me too!