Oh my.... Feminists' heads are exploding all over the world right now.
Of course it's much worse nowadays, but even back then when the first season was on the air, there was some apparent criticism of Sesame Street's gender and racial stereotyping, which I believe is documented in the 1971 book "All About Sesame Street". That lead to Susan, for example, getting a job as a doctor sometime during the transition from the first to the second season, to break away from the perfect housewife mold.
Complimenting the song about Mothers, there was also one about Brothers and Sisters, which was featured around the same time on the LP "Susan Sings Songs from Sesame Street," which also has some gender stereotypes. They're not quite as cringe worthy, but even when they are, the blow is softened with the final lines, "Still I like my brother fine, and I'm glad my sister's mine".