The husband-and-wife songwriting team of Carole King and Gerry Goffin wrote this song. Little Eva was Eva Boyd, the babysitter - actually more of a nanny - being paid $35/week to watch their daughter Louise and clean the house. They were all young: Eva was 17, King 19 and Goffin 22. One day King came up with a melody that Goffin thought sounded like a locomotive, and when he saw Eva dancing with their daughter to the tune, he got the idea to make the song about a brand new dance - The Loco-Motion. He wrote the lyrics and they brought Eva to the studio and had her record the song as a demo - they were hoping Dee Dee Sharp would sing it. Their producer Don Kirshner thought Eva's vocal was just fine, so they named her Little Eva and had her record the song. The only downside for King and Goffin was losing their nanny: when the song became a million-seller, Eva was able to buy a place of her own.
Gerry Goffin had actually had this song idea in the back of his mind for a couple of years, but had never found the right moment to bring it out. When he sat down to write it at last, he defended it to Carole: "This is going to sound stupid, but what the hell." Don't all the biggest fads start out that way?