Not all these kids learn these words at home. It can be learned anywhere where a person might use such a word. It is just as likely that she heard the word anywhere, perhaps even another child at that daycare.
There are plenty of meme like bits of “information” hanging out at school passed on from one grade to the next; not unlike a virus. They are not part of the official curriculum imparted by the staff, but are passed around by the kids in their daily interactions. Only separation of the kids prevents inter-generational transmission.
“...only the ones who hear the words at home.”
It might depend, to a certain extent, on the age of the child, but when you grow up in the big city as I did you hear plenty of words on the street that you’ll never hear at home.
Still, it seems silly to me to eject a child from a school for one verbal infraction. She’s an imperfect person, like the rest of us. Person in training, you could even say.
Spot on. Nobody speaks without thinking.