Crying stretches babies lungs ?


My MIL says that newborns need to cry to stretch their lungs. All my sister in laws say Now I don’t want to leave my LO with any of them. Has anyone heard of this? the same thing. My sister in law is in town and my husband wants her to keep the baby to “give me a break”. But I’m worried that they’re going to let my 5 week old baby cry unnecessarily.