Can the bio mother give the daughter the non bio dads last name without informing the bio father of the child? Bio dad never knew about the child (now 15 yrs.old) until about 3 months ago. The non-bio dad knew he was not the child's father at the time of birth and was not listed on BC. State is Wisconsin and the bio mom states they want nothing from bio dad. just that the daughter wants to know who the father is, but with some of the emails he's been sent,it seems as though they are "pushing" him into a life with the child now. Bio dad, has gotten married and has raised 3 kids that are not his as his own already. Don't they have to file some type of form to do this and if they have without informing the bio dad, isn't this illegal?

They must attempt to get the bio dads permission for a name change. The only time that would differ is if the stepdad is also the husband at the time of birth. The he would be the legal father regardless of the bio father. The only thing the bio dad could do is contest parantage if that were wanted.

So it mostly depends how the situation went down.

Well they did not get married until after the fact the child was born. He still is NOT listed on the BC but they did in fact give the child his last name. I do not know what they filed but I was told by the mom that they filed some type of paperwork.

Oh, and from my understanding, they did NOT do an adoption process for the child. So am I safe to assume he has taken all parental resposibility at this point?

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Legally if a mother is not married she may give any last name to her child.

If they married within a specified time frame after the birth then the husband would be the legal father.