Oh, come on. What mother did not already know this?
Yup. We sang a Welsh lullaby to our children in the womb so it would have a more calming effect on them when we sang it to them after they were born. This helped a great deal when we wanted them to sleep. This has long been a tradition in my family - my father got it from his mother, and passed it on to me, and his mother got it from hers.