Here are clips from Sesame Street episodes that talk about breastfeeding…

Buffy breastfeeding Cody, from 1977:

Maria breastfeeding Gabriela, from 1988:

Moving away from Sesame Street for a moment, Mr. Rogers also talked about breastfeeding in Episode 1536 from 1984 (the nursing section starts about 2:40):

This song by Joe Raposo from the mid-1980s also shows a breastfeeding baby. Apparently the song has been updated and the breastfeeding clip was replaced with a baby being bottle-fed.

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Nursing mammals from Sesame Street:

Tandem nursing on Rugrats….

Enjoy!