Your child needs a U.S. Passport to travel overseas as an American Citizen.  To obtain a passport for a minor, you apply to the U.S. State Department using Form DS-11.   By waiting until you have a Certificate of Citizenship ("COC")for your child, you will not have to send in your original foreign adoption paperwork — only the COC.  You will, however, need to bring all the original foreign adoption paperwork with you to your local Passport Processing Office (such as a county clerk office or a post office). 

For more information, please visit the U.S. State Department—Passport Info Website.