@shelbilynne, my mother in law told me that when I had my son (he was a premie) he smiled all the time in his sleep, even while in the nicu... she told me that and I about burst into tears.... I really think that's what it is... I mean most babies wake when you speak to them, my daughter just keeps smiling when I ask "is (relatives name) talking to you?"
I have been told it's the angels whispering to them 😇 I always ask my daughter when she does it if it's certain family members who have passed (she never wakes up when I ask either lol) @shelbilynne