Stimulus payment reclaim - Help!

Just found that only children with valid ssn can get the stimulus payment. We have filed the tax return on eaily April and have not got the payment yet. Is it possible to reclaim the payment? We have be charged so much tax, and just get this little rebate... so sad. Today, I have gone to the ssn office to apply for my children. Should we wait until the notice or sent the SSN number immediate after we get it? where can I find information about reclaimming? Thanks for your help.