Can my common law husband claim my children as his step children? Can he claim head of household if I didn't work and he supported all of us all year?

[TaxGuyBill]

If he is now your legal husband, for tax purposes, your children are also his children.

No, he can not claim Head of Household.  The choices are Married Filing Jointly or Married Filing Separately.  In most cases, filing Jointly has the best results.

[macuser_22]

But be sure that you are really common law married.  Only a few states recognize common law marriage and each has it's own rules.

[lrk83]

We live in South Carolina. We have bills together bank accounts and call each other husband wife. I even use his last name on few things. Is that enough to claim it?
What is the reason if I may ask that he couldn't do head of household?

[Zbucklyo]

South Carolina does recognize common law marriage.  Make sure you meet the requirements to be considered common law married under South Carolina law.  In that case, @TaxGuyBill provided the correct response.  And Married Filing Jointly is a better filing status than Head of Household, so it is to your benefit to file that way.  But your husband may not file as Head of Household; to do so, he would have had to have lived apart from you for the last six months of the year, and be able to claim your children as dependents.