I went to claim my kids on my taxes and it came up that somebody had already claimed them without my knowledge. How do I find out who claimed them?

Contact the IRS. Are you divorced? Could your ex have claimed them?

The main thing you do is get it cleared, prove they are with you, so you will get the credit for them. The IRS knows but they may not tell you, but will investigate it thierself.

But it has to be someone you know and someone who has the kids social security numbers. So it has to be someone very close to you or someone you gave all that info to

I will both agree and disagree with Chuck here. Yes the IRS may not tell you who, but they will investigate. So you make an appt and go down there with your proof that you provide more than half the support for those kids. If you prove you are entitled to, they will go after the person who claimed them. You may never find out who it was.

While the likelihood is that it is someone you know, with identity theft rampant in these times, there is the possibility that this is what happened.

Both Scott and Fr Chuck covered the pertinent points. I have nothing to add.