Stockton-on-Tees Borough Council

I didn't know a birth could be re-registered. What does it mean? The baby has my boyfriend's surname already.

The re-registration of a child has nothing to do with the surname, it is to do with the Legitimacy Act 1976. If the natural parents of a child were not married at the time of the birth, and subsequently marry each other, the child automatically becomes a child of the marriage, and the re-registration is so that the birth entry (and any subsequent full birth certificate) reflects the fact that the child is a child of the marriage. You will need a form LA1 which both of you will have to sign, but only one of you will need to attend the office to re-register the birth.