Wikipedia: https://en.wikipedia.org/wiki/Little_Willy_(song)
"Little Willy" is a song written by songwriters Nicky Chinn and Mike Chapman and performed by the British glam rock band The Sweet, released in 1972 as a non-album single in the UK, peaking at #4 in the best seller charts. It was released in the US in September 1972[6] and also appeared on their US debut album The Sweet and became their biggest hit in the US, reaching #3 on the Billboard Hot 100.[7] Billboard ranked it as the #18 song for 1973.
In a retrospective review of glitter rock, Bomp! noted that although rock music journalists almost uniformly "loathed it", the song was a huge commercial success and "helped launch the essential glitter rock formula sound".[8]
"Little Willy" was used extensively in the pilot of the television series Life on Mars.
AllMusic:
https://www.allmusic.com/song/little-willy-mt0002312076
Sweet's first major American hit single, "Little Willy" trails more playground innuendo than most people could fit into an entire album, let alone a three-minute pop song. It is, naturally, utterly irresistible, a chanting, stomping ode to -- well, that's best left to the imagination -- its wild, singalong chorus as infectious as any of the band's earlier releases, but, like "Poppa Joe," laying over an arrangement which is moving closer and closer to Sweet's own sound. Indeed, although the group itself was once again not required to play on the record, this would be the last time that happened, a pledge that the distinctly Andy Scott-styled guitar line makes plain. Sweet, incidentally, hated the song. Nicky Chinn recalled: "Michael and I were definitely autocratic with our bands, and I became aware of that when we were told [by Sweet] that "Little Willy" was a piece of rubbish and had no right to be released. It wasn't exactly a symphony, of course, but...it was a hit, and we told them it was going to be released whatever they thought of it."
It's pop-rock. It's bubblegum. But that was often an element of glam rock -- think of T.Rex.
It was very good pop-rock, though. An earworm. And as silly and superficial as it is, I think it's held up over the years much better than some of the more pretentious music of the time.
From Songfacts:
https://www.songfacts.com/facts/sweet/little-willy
This song was written by Nicky Chinn and Mike Chapman - neither of whom were members of Sweet. Instead, Chinn and Chapman were a major force in the British pop music industry in the 1970s. Just as in the US, Leiber and Stoller became known for "the Brill Building sound," Chinn and Chapman in the UK became known as the "Chinnichap" sound. They produced songs for Suzi Quatro, and British bands Smokie, Mud, Racey, and The Arrows. Chapman would later produce albums for Blondie and The Knack, and along with Holly Knight, wrote Pat Benatar's hit "Love Is A Battlefield."
"Little Willy" was Sweet's biggest US hit, peaking the charts at #3 when it was re-released in 1973. It was a non-album single, but went gold in the US and UK all by itself anyway. Critics in the UK dismissed the song as "bubblegum" and referred to the lyrics as "nursery porn." Sweet wanted to shed their bubblegum/ glam-rock image and become more hardcore, so they later turned to writing their own songs.
Putting this song together, Chinn and Chapman used a pounding drum beat popularized by Slade and producer Mike Leander. They mixed in the riff from the Who song "I Can't Explain," and added the exceptionally catchy chorus, which dug into your ear and wouldn't let go. The song didn't tell any kind of story - just that Willy won't go home - but listeners didn't care and with Glam Rock, the lyrics weren't supposed to make sense anyway.