Hi, I'm from American Samoa and I just recently found out that someone else has been claiming my children on their tax. How can I find out who that person is? What should I do if I find out?

To start with... do you clearly have full legal custody... and were you ever divorced from their other parent?

You cannot. What you do is file your return and include proof that you are the one legally able to claim them on your taxes. The IRS will investigate and take appropriate action.