From our experience, after you have registered the birth in Ethiopia; if you are mix family (habesha and other; us) you will need to get a form from the Embassy and have this notarize at the embassy if you and your significant other are living together thin this should be easy, but if not there is another step, you need to go to the USCIS home website and print the form out, also follow the directions listed on that form; it will cost around 12,000burr to complete everything because you will need to get the child's first passport as well. thought fees are due to change from time to time, so the best thing to do is: (1)after receiving your child's certified birth certificate, you should get Form DS-2029 (photos.state.gov/libraries/libya/19452/public/DS-2029_report_of_birth.pdf)
2) look on the USCIS; website and print this form out if this one will not open or google "Form DS-2029" if your in Ethiopia you best bet would be to go to the Embassy; ask for this the same form thy will walk you though the process.
3) make shur everything is in order and all addresses are correct you file for the Social S'Card separately and it can take forever (don't worry if it takes more than 5months; its normal)
4) its important you do the affidavit at the embassy, unless you and the child and mother are living other country; (ie) Ethiopia and other in home country, than you know any place will do affidavit (UPS-Store) is the best place.
5) Follow instructions listed on the form to make secondary chick and as will as all supporting documentation; file with the Embassy (average time for new birth certificate is about 2-months but its by work load so expect 3-months out to be safe for passport and everything, social s'card-well that's something you should do in the states if you can, or just wait the time-out...
This is the best information I give you all for now; happy birth for all you out there with many blessings!