Most important, not to put your name on birth certificate, cause if a paternity test is done which is not unheard of at embassy level, and results show you're not the father, you will have bigger issues, and most likely a denial will be issued on the visas.
You should consult a US immigration attorney, these agencies such as you named, mainly lick the envelope and send the paperwork. Doubt they will assist you on this matter with a child involved that is not even yours.