It's A ...Baby

My neighbor recently had a big party and draped across her garage door a banner that read, "It's a boy." She wasn't pregnant, as far as I know, but she has a married daughter, so, I figured the daughter had a baby.

There is just one problem. Four weeks earlier there was another big party and that time there was an "It's a girl" banner on the garage. I didn't take a picture that time because, who cares? Now, it's a mystery.

So, what is going on? My neighbor has no other children. Were they twins born a month apart?
Did they get the sex wrong and realizing their mistake, decide to have another party to get boy stuff, instead of frilly, pink girl stuff?