Genesis 4:26

And to Seth, to him also there was born a son; and he called his name Enos: then began men to call upon the name of the LORD.

1. Seth apparently married, for he had a son named Enos.
2. The bible doesn't include every detail.
3. People, in general, were apparently not praying prior to the birth of Enos.
4. Prayer is better than not praying.