I have a 4 yr old son who wants to change his last name to my married name, and the name of his daddy. The bio-dad is not on the birth cert... I was wondering if I can change it without the formal consent of the bio-dad, especially since the bio-dad is not in any way shaped or form involved in my sons life.

Thanks

Short Answer... no you cannot.

Yes you can... if you live in California that is, you just go down to the records office and say you want to change the birth cert. there is a small fee but its not much and since there is no bio father listed or a bio father acknolging he is the father you can change it.

That is incorrect. First, we do not know where the OP is located, so we cannot give an answer pertaining to a particular state. Especially when it is completely wrong. Some states will allow a minor revision to a BC (like spelling of a name) but a legal name change involves a court order. A court order for the name change of a minor in CA (since that is where you cited) requires the consent of everyon with legal rights to the child, including the father. A father who is not listed on a BC has the same legal rights as the mother, he simply has to go to court to have those rights enforced. A name change in this situation would be more difficult, as she would have to locate the father, establish him as the legal father, and then gain his consent.