Ferraro, who started at “Sesame” right out of college as a secretary and has now been a writer and lyricist there for 26 years, is responsible for one of Elmo’s most popular numbers, “Brushy Brush,” a celeb-filled ode to brushing your teeth. It has nearly half a billion YouTube views, and the gratitude of legions of toddler parents.

Cerf is known for his rock parodies: He was behind the Grammy-nominated “Born to Add,” a Bruce Springsteen take-off featuring Bruce Stringbean, with Cookie as Clarence Clemons on the album cover. (Though “Sesame” normally has its choice of stars, there are some that have remained out of reach. Despite entreaties, the Boss has never appeared. Neither has Madonna, Paul McCartney or the Rolling Stones.)

Image Bill Sherman in 2015 at his home studio, where he did a lot of composing for “Sesame Street.” Credit... Jeff Zorabedian

After a song has lyrics, Sherman and his team score it. Brevity and repetition are key; “Sesame” songs are mostly just verse and chorus, but they’re tuned for catchiness. “You try to make the verse a hook, and then the chorus even more earwormy, if possible,” Sherman said. Demos go to producers and artists for approval and production suggestions, but they must also pass the ultimate litmus test: his two daughters, now 6 and 8.

“They’re very honest, and if they aren’t humming it or singing it, I will usually throw it away and write it again,” he said.

His track record is stellar: “What I Am,” the first song he co-wrote, for Will.i.am, became a viral hit, with more than 88 million views, and won an Emmy. A number for Janelle Monáe, “The Power of Yet” — inspired by her hit “Tightrope,” and written “in my basement in like 20 minutes” — was so convincing that she told him it could appear on her next album. From musicians, said Sherman, that’s “the best compliment I ever get.”