Unfortunately, you can't sue the government for giving you bad advice. You have to take some responsibility for knowing the laws and double-checking with an immigration lawyer, for example.
You could possible claim the credits for 2020 if you had a valid extension and you filed late, or have not filed yet. You must have a valid SSN for each child on a "timely filed" (on-time) tax return, that means filed before the regular deadline, or filed before the extended deadline but only if you have an extension first.
If you file a timely 2021 return with the children's SSNs, you will be eligible for the enhanced child credit for 2021 as well as the $1400 round 3 stimulus rebate.
