Do You Allow Your Kids to Listen to Mainstream Music?

A song lyric containing a swear word slipped from my daughter's lips the other day, and I was taken aback. At four, she loves music and listens to it daily. But since lyrics blare just about everywhere — on the radio, in people's cars, at the mall, and on television commercials — it's hard to edit everything my kids hear. Do you go with the flow or try to censor sound?