Old wives talE?
I'm not sure. My daughter never acted any different.
And my second was a boy. Now pregnant with my third and both kids... well they act the same as always.
If your child is behaving a little differently, it could be jealousy?? Hearing mommy & daddy talking about another baby can make them feel a little... idk pushed away in a way?? Even if your giving them all the love in the world.
I decided to take a pregnancy test with my second because my first would lift my shirt up and kiss my stomach. I thought it was cute and my husband would say "imagine you're pregnant and that's why he's kissing you?" And we'd joke about it because we weren't TTC or anything, test came out positive. My son also would be stuck on that "baby was gonna be a girl" even when people would say "maybe it's a boy" and I had a baby girl.
Idk if it was just a coincidence or something..