sing (one) to sleep
To help or cause one to fall asleep by singing. My daughter was really upset from her nightmare, so I sang her back to sleep with a lullaby my own mother had taught me. The performance was so lackluster that he actually ended up singing several people to sleep.
sing someone to sleep
to sing softly and sweetly to someone until sleep comes. The mother sang her baby to sleep. Please sing Timmy to sleep. He is very restless.