Melanie,
No cost to file G-884 or the G-639, and you should do both. I have samples and step by step directions for both should you need them. Email me and I can forward the info to you.
You can file at anytime. For G-884,You will need to email USCIS at:
Child-Citizenship-Act@dhs.gov
send child's name on entry and the A# from your COC, also on the passport/visa. Ask them who currently has your file and where you should mail to. They usually respond in 24 hours.
Good Luck!
cborsa7@yahoo.com