"Mammas Do n't Let Your Babies Grow Up to Be Cowboys" is a country music song first recorded by Ed Bruce, written by him and wife Patsy Bruce. His version of the song appears on his 1976 self-titled album for United Artists Records. In late 1975 -- early 1976, Bruce's rendition of the song went to number 15 on the Hot Country Singles charts. This song was featured on Chris LeDoux's album released January 20, 1976, Songbook of the American West, and in the Grand Theft Auto: San Andreas video game soundtrack, on the fictitious radio station K-Rose.

Who sings mama dont let your babies grow up to be cowboys? OK. Let's think. My stream of consciousness:
The relevant sentence in the passage is: "Mammas Do n't Let Your Babies Grow Up to Be Cowboys" is a country music song first recorded by Ed Bruce, written by him and wife Patsy Bruce. The answer is Ed Bruce.