How to apply SSN card for my son after green card?

Hi,

Does anybody how to apply for SSN card for new immigrants? As we just found out that if you don't have a SSN, you won't get the most recent Federal Tax rebate. In my case, my son has a tax number, but he does not have a SSN so we won't receive $300 tax rebate for him from IRS. Apparently, the government treats non-immigrants differently. If you don't have a ssn, but you are qualified to get one. Now it's the time.

thank you in advance for answering my question.