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Can you get your foreign birth certificate?
I don't think I can.
what if I can't get some of the documents I'm asked for?
For any document you don't have or can't get within 10 days, we'll ask you for some other document. Any document submitted must have your name, your birth date, identifying information and a recent photograph.
In my case, I  lived abroad for quite some time. Do I need to do something else?
You can show any document that proves you lived abroad for a long time and you don't have a social security number. You could use your previous or current passport, school or employment records, etc.
and for children, do they have to attend personally when asking for a social security number?
If they are older than 12, yes they have to be present during the interview.
and if I have lived in the US what other information do I need to give?
You could be asked for information about the schools you attended or copies of tax records that'd show that you don't have a social security number.
Now, for adults wanting to get the card for the first time as foreign-born citizens?