Hah! I thought I remembered seeing a version of "Yellow Submarine" on Sesame Street. Thank you Youtube.
This is absolutely perfect of course, because McCartney wrote it (with some lyrics assistance from Lennon and Donovan) as a children's song.
This was my introduction to the Beatles - until I was in seventh grade I was vaguely aware of the Beatles as the band that did Yellow Submarine. And then I heard "Live and Let Die" and found out that it was performed by Paul McCartney and Wings, and they had a new album coming out, Band on the Run. And then I finally made the connection between Wings and the Beatles and got myself a copy of Sgt. Peppers, and the rest is history.
The early 1970s was the nadir of the Beatles' reputation, it should be noted. They had only recently broken up and were considered old news, basically, although Elton John was kind enough to remember them with his (far inferior) version of Lucy in the Sky with Diamonds. And Anne Murray did a version of "You Won't See Me" - the first rendition I heard of the song. Rosemary Watson, my classmate in seventh grade loooved Elton John and Rita Sutter, Lynn Kosek and I tried to tell her that Elton John was gay, but she wouldn't listen.
Of course they were rightfully restored to the Rock n Roll pantheon by the 1980s, but I do remember the period of time when the Beatles were considered has-beens.