I was little in the 70's and 80's when Johnny Cash was really popular. But back then he was popular with a certain demographic and it was not as wide spread as his popularity is now. Mr. Clean had never listened to him as a kid, nor did his parents. But we did.
My parents could best be described back then as "hippie bikers". They were not granola eating, tree hugging hippies, but were not Hell's Angels either. They fell in the middle. They also were not believers at the time. So the music they listened to was never censored for my little ears; but in their defense, if it was played on the radio, it should be fine. Right?
I knew the words to Cash's "A Boy Named Sue" by the time I was three or four and sang them with conviction. I also knew the words to "Man Eater", by Hall and Oates and found out exactly what Cyndi Lauper meant in "She-Bop" at the ripe old age of 9 when it was released (read the lyrics and you will too, and might be quite taken back; it's not the silly little nonsense song many thought it was).
Johnny has a renewed place in our family's vast musical collection and Mr. Clean has dusted off many of my Johnny Cash cds as well as gotten his own, but "A Boy Named Sue" does not get any air time when the children are around. Thankfully Mr. Cash later became a believer and released many songs appropriate for a different audience.
Pay attention to what your children listen to, as it will stay with them for a very long time. I can still recite every word to quite a few "Top 40" hits played by the ever so faithful Casey Kasem and Dick Clark. Most of them had no redeeming quality whatsoever, yet the words will still pop into my brain from time to time 20 years later.
On an aside, for a little nostalgia, check out this Sesame Street clip with Johnny Cash and Oscar the Grouch. No politically correct children's shows for my generation! Thank goodness...