I agree with C R S. Hold onto the Green Card for now. If your family decides to apply for N-600 USCIS will likely ask you for the Green Card, or to send them the Green Card. Funny thing is that when I got the certificate of citizenship for my child (through form N-600) they sent a letter in the same envelope saying that there was an envelope to send the Green Card. I could never find the envelope, so I haven't sent anything and I am holding to the Green Card until I get a corrected certificate (that's another story). By the way, this post was quite off topic for this thread.