I think it's totally valid for Sesame Street to teach about breastfeeding on the show. It's a natural thing that happens in life, and kids should learn about it at a young age.
What exactly do kids need to learn? It's been my experience that children don't tend to have questions about breastfeeding, they just accept it. Unlike adults whose views have been skewed, children already see it as a natural thing. I don't think the point of having breastfeeding on Sesame Street is for the kids, it's really about making breastfeeding a more acceptable practice in our society.
Understand I'm a strong supporter of breastfeeding in public. I've done it, it's no big deal. And I'll always support a mother if she chooses to feed her baby in public by breast or bottle (they get critized too). If Sesame Street wants to mention it, cool. If not, that's ok too. Making breastfeeding a more mainstream topic is always a good thing, I just don't know if Sesame Street is the best venue. It's not as though I sit down with my kids on a regular basis on go over the benefits of breastfeeding as if I were reinforcing their ABC's. Now showing a mom breastfeeding on American Idol that might get people's attention.
Perhaps Sesame Street should focus on a greater appreciation for the human body in general. Let's stop little girls from thinking that the women they see in magazines are real. That it's not all about having the perfect body, the perfect hair, etc.