I must admit, my sister-in-law gave me that exact same book when my daughter was around the same age! Ironically, I'm a raging liberal, and my sister-in-law is pretty far to the right! LOL! Now, as liberal as I am, I was pretty surprised by those lyrics as well! Mostly, because I thought they could lead to some uncomfortable questions. This ended up never happening. In fact, now that my daughter is in kindergarten, one of her friends at school DOES have two dads! My daughter STILL hasn't asked me about it. I guess the questions will come later. Or she just accepts it and doesn't think it's different. Oh, and BTW, that song was initially on Sesame Street, I believe.
Personally, I wouldn't edit my music based on whether it offends someone. My attitude is, if it offends, then I really wouldn't want to be friends with them anyway! LOL! But then again, I am a raging liberal! You have to do what your comfortable with. Frankly, I think the message you tried to impart was a good one. And again, the song was on Sesame Street!
That's my two cents!
C.
www.littlebitquirky.blogspot.com