About a week ago we were invited to a Christening and before I had a chance to buy an acceptance card and send it off, the mother asked if I had received the invitation and whether or not we would be coming. I was surprised at how forthcoming she was but said yes, that we would be going. But the question is, should I now send the acceptance card as a formal RSVP? I'm happy to send the card now that I've bought it, just wondering what etiquette dictates - I want to get it right!!