Definition & Meaning of "[sleep] like a (baby|log)"

What is the origin of the idiom "sleep like a baby" and when to use it?

The origin of the idiom "sleep like a baby" is believed to be a relatively recent one, originating in the 20th century. The expression conveys the idea of sound, undisturbed sleep by likening it to the peaceful slumber of an infant. On the other hand, "sleep like a log" has older origins, dating back to the 17th century. This idiom likens restful sleep to the motionlessness of a log, emphasizing the deep and uninterrupted nature of the slumber. This idioms is used to reflect on the universal desire for peaceful and undisturbed sleep, and they have been used for centuries to describe the quality of one's rest.