It's fun to send gifts, and it makes them happy, so I wouldn't try to stop that. Let them pamper you if they must.
You might try asking them to spend less, though. Tell you you appreciate their thoughtfulness, but that the costs of the gifts makes you uncomfortable. if they must send you gifts, ask that they be lower cost gifts, or that you are consulted with for anything over X dollars.
oh, and the answer to your question is: as soon as you acquire a younger sibling. Is that likely to happen anytime soon?
