But issuing a birthday invitation is just that, an invitation, not an obligation. If a friend (or even a mere acquaintance) overenthusiastically invites you to her child's birthday party, when you're not very close to the child, that, it itself, is not a breach of etiquette. You politely RSVP that you have other plans, and send a card if you feel like it. It doesn't matter if your other plans amount to a good book and a glass of wine; it's rude for her to inquire about that anyways. If she's pushy and acts hurt because you can't attend, then she's being rude and you have cause for complaint. If she expects you to help pay for the party, that's tacky; so are lightly veiled demands for gifts. But sending an invitation, all by itself, is a sweet gesture to people who might be interested in celebrating the kid's milestones.