I get that I truly do. And that's exactly why the educators behind Sesame Street have always wanted a diverse human cast (race, sex, ability, etc.) to teach tolerance at an early age. That's also why they have targeted obesity. Start healthy habits young. And for those things sending an early message works. But I don't see the issues surrounding breastfeeding in public on the same level as say discrimination or eating too much candy.
I always felt the healthy habits bit was damage control for having McDonalds as a sponsor.
Aside from that, I completely agree... some things are for young children to know, others aren't. Breastfeeding seems like something adult parents could talk about, and I kinda have a feeling that if they talked about it retroactively, like "That's what Mommy did to you" it may confuse kids who were bottle fed.
Still, the problem isn't the subject matter, it's the show. More specifically the tone of the show currently.
However, I can see Sesame Street talking, not so much breastfeeding, but rather about how baby animals get milk from their mothers, and liken it to breastfeeding... sort of as a "humans aren't all that different from animals" type biological/nature lesson.
Still, we just don't have the luxury of Big Bird asking what grown ups are doing unless it's directly related to a curriculum based plot line. And that would mean it has to deal with science, trial and error, nature, healthy habits, multiplication and more complex math concepts... all that stuff. The likening human breastfeeding to how calves get milk from the mother cow is as close as the curriculum would get.