It's not expected that a baby be invited to parties.
Joseph is throwing a big party for all his friends and is sitting at the dinner table making invitations.
Joseph wants to invite the Davis family to the party.
Joseph writes a card to Baron and Bette Davis and invites the two of them over.
Joseph writes a card to Baron and Bette Davis and their infant son, Glenn.
Baron and Bette Davis are both delighted to be invited to the party and look to book a babysitter for the night.
Baron and Bette are both mildly insulted that Joseph thinks they'd bring a baby to a party.