The b word

I don't know where the idea of "bad words" came from.  How does a word become bad?  Are they created as bad words or does society's use of them make them bad?  Whatever you believe, this idea is something that has been rather comical to me as I watch my six year old try to create meaning out of what words are "bad words."
On the way home from school the other day, Kinsey says to me, "Mom, two boys in my class were saying the 'D' word."  Of course my mind goes to the worst possible words that can be created using d as the first letter.  With much hesitation I asked, "Kinsey, what word were they saying?"  Part of it was pure curiosity on my part, the other part was wondering how much damage control I was going to have to do with her.  She said, "If I say it, do you promise I won't get in trouble?"  I assured her she wouldn't.  "But do you really promise you won't be mad?"  I assured her once again.  She looked down and in the lowest voice possible, I heard her mumble, "They said dummy."  Relieved, I explained that yes, that is a very hurtful word.  And we shouldn't say it.
I would say that we are very protective of the TV shows that our kids are allowed to watch.  We don't let them watch Sponge Bob or Nickelodeon at all.  Yes, we shelter our children.  Very much.  So imagine my surprise when Kinsey comes to me and informs me that a new show on Disney said the 's-h' word!  My immediate thought went where yours is probably going.  There is only one bad word that I know that begins with 's-h'.  And I was shocked to hear that it was said on Disney.  However, to Kinsey the bad word was 'shut up.'  Which is also not something that we say in our house.  I tried not to laugh but was very relieved when I realized that her view of bad words was a bit skewed.
In the car one day, both girls were bickering back and forth about something.  All of a sudden I heard Kinsey start crying and saying, "You can't say that!  Mom, Kaitlyn called me the B word!"  I nearly pulled the car over because I was so taken back by this comment.  I asked Kaitlyn what she called Kinsey but she would not repeat what she just said.  Given that she refused to utter the b word again, I couldn't believe that she really did say it.  So I made Kinsey say it just to be sure.  I said, "Kinsey, what b word did she call you?"  Through tears and sadness, Kinsey blurts out, "BABY!  She called me a baby!  That's a bad word right?"  Holding back laughter, I validated Kinsey's thought that yes, it wasn't nice to call people a baby.  But I was very glad that Kaitlyn didn't call her the b word I thought she said!
I realized that my children probably wouldn't know a bad word if they really did hear one.  Jason and I don't use that kind of language so how would they know?  When they do hear a real bad word, I bet they will come home and use it the same way they heard it used but won't have a clue what they are really saying.  Is that the downfall of over-sheltering your kids?  I know I can't keep them thinking that dummy, shut up, and baby are the worst words in the world to say and hear.  I'm sure they'll get it all figured out one day.  I just hope it's not until they are about 30.