My husband and I became common-law married 7 years ago. We have now separated. He lives at his parent's house. I live at our home with our children. He changed the locks on the house while I was at work, (I broke back in per police suggestion) and he has my two older children (8yrs, 10yrs.) and will not bring them back to me. I have our third child. (1 yr 7 mo)
He has taken my birth certificate and my social security card and will not give them back. He has also taken the children's birth certificate's and social security cards.
He currently has two domestic violence charges against him, filed by me. He involved our children in one of the scuffles so we were both placed on the child abuse registry.
What can help me get my children back and protect all of us from him?

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What can help me get my children back and protect all of us from him?

Get a lawyer and go to court seeking a child custody and support order and a domestic violence restraining order.

You didn't ask about the SS cards and the BCs. Easiest thing to do there may be just get new ones (and hide them).

At this point and time, he is the father and has just as much legal rights to have the kids as you do.

And to be really rude, you had no issue leaving the kids with him, and living with him, even after the domestic violence charges, since you were with him till he locked you out and took the kids. So it was no "issue" before since you were living with him still, but now you have issues with it.
Why did you not leave him when there was domestic violence, esp with kids??

Next you will have to file for a custody order for the kids.
Also I will assume you live in a location that accepts common law marriage, there are fewer places that has it.

... Also I will assume you live in a location that accepts common law marriage, there are fewer places that has it.

Right. But, married or not, OP needs to go to court to get a custody order anyway.

ANY question on law needs to include your general locale as laws vary by area.

Common law marriage has largely been done away with. So are you sure your area supports it?

He may have broken the law by locking you out.

So you really need an attorney to know what rights you actually have.

As the others have stated get a lawyer and file for custody of your childeren. As for your social security card and birth certificate, you could go to the police and file idenity theft charges against him, if you wanted to be mean about it. As far as getting your children's documents back there is noting you can do without being awarded full custody of your children in court.

as for your social security card and birth certificate, you could go to the police and file idenity theft charges aginst him, if you wanted to be mean about it.

This is not correct. There is no instance of identity theft unless he USES the documents to create some type of account. Just holding the documents is not identity theft.

In my area being in possession of idenity documents and refusing to return them is considered intent to commit idenity theft and is treated as idenity theft, this may not be true everywhere.

Comment on ScottGem's post
In my area being in possesion of idenity documents and refusing to return them is considered intent to commit idenity theft and is treated as idenity theft, this may not be true everywhere.

Please cite the law that supports this. I would suspect, if such a statute exists, its to support someone being caught with stolen documentation being charged with a crime. If so, it would certainly not apply to a father having his children's documentation or a husband be3ing in possession of a wife's. Knowing statute is one thing, knowing how it would be applied is another.

... as far as getting your childrens documents back there is noting you can do without being awarded full custody of your children in court.

Really? I can go to the vital statistics office of the state in which my children were born and get copies of their birth certificates. With those, I can go to the Social Security Administration and get replacement Social Security cards for them. And since my wife and I are still married and living together, it is not currently necessary (or even possible) for me to be awarded custody in court.