In many areas now a parent doesn't have to register their child to get the ss card whether they are Amish or not.  Now how it works, the birth certificate is signed and filed by the midwife, doc, or whoever delivered the baby in most cases. I'm sure there are exceptions.  The ss cards for the new baby come in the mail. This has been in effect in some states since the 70's.

Anyone born in the US now with a registered birth certificate gets a ss # off the bat

1) they have too not only for tax purposes but because of Homeland Security Rules that went into affect after 2001.  

2) This sounds cruel but they are checking for "anchor" babies so to speak  and that baby's ss # is either going to tie into a mother or father with a false number or no number at all.  This is how many illegals in some areas have been caught and deported.

Far as FICA many people can opt of it and it doesn't have to be for relegious purposes. For instance many men who work for CSX railroad don't pay into SS they pay into Railroad retirement benefits instead and have their own inhouse system.

Anyone born in the