It's best to start a new thread...

http://www.ssa.gov/pubs/EN-05-10084.pdf

"Online my Social Security account
Social Security has an easy-to-access, easy-to-use
web portal for some personalized online services. At
my Social Security, you can create an account if
you are age 18 or older, have a Social Security number
and have valid E-mail and U.S. mail addresses. Go to
www.socialsecurity.gov/myaccount and provide some
personal information to verify your identity. Then choose a
username and password to complete creating your account.
You can use your my Social Security account to access
your Social Security Statement to check your earnings
and get your benefit estimates. If you receive benefits, you
also can:
• Get your benefit verification letter;
• Change your address and phone number; and
• Start or change your direct deposit."

If you haven't signed up for an online account, that might be helpful.

I believe you mean SSDI benefits not SSI, since SSI does not have Survivor Benefits.

If you can't get a time frame for your first payment from a rep at your local SS field office, you might insist on speaking with a Supervisor. If you are in danger of eviction or having utilities shut off, you can make a Dire Need request to speed things up. If your son's father has other children it might be taking longer for the Payment Center to confirm how the benefit needs to be divided.

One last option is to contact your local Congress person or Senator and request help from his or her staff.