The idiomatic expression “to sleep like a baby” is one that I didn’t used to question. But after further examination, I realized that this idiom doesn’t make any sense at all.
After a long day of hard work, people often say, “Man, I’m going to sleep like a baby tonight.” If that’s true, they are going to be pretty unhappy come the morning.
Babies are known to wake up for middle-of-the-night feedings and diaper changes. They’re also known for waking up in tears, which is a problem I doubt most idiom-users encounter.
Babies are not the deepest of sleepers. They’re quite light sleepers, in fact—just think of how quiet everyone in a house needs to be after a baby is put to bed.
So, unless you want to be fussy and tired the next day, you probably don’t want to sleep like a baby.