Babies laughing / smiling in their sleeps

In Punjab there is a belief, if a baby less than a year old is laughing or smiling in their sleep it means they're speaking with God, where the origins of our Soul belongs to. God asks "Are you happy?" They say "Yay" or "nay" dependant on surrounding and how well they're being looked after by parents/ carers.

Of course, am sure there's a Scientific reason per usual (God loves to hide behind Science/ Psychology) of WHY babies laugh during sleep.