How do I change my children's names to mine bothe there dads are on birth certificate but haven't had a thing to do with them I am with a new partner and am having another baby I want them all to have my name so when they start school its not complicated do I need the fathers permission

It Depends upon the Country norms! If Demands you will Have too!

I also want to change my daughter's last name to mine because her father hasn't ever been in her life and has never done anything for her.

I have been told that I have to have him sign for the name change. I am located in the US. I don't know about the laws in other countries though.

Requirements for Name Change Order: For an order of name change to be granted, the court must find (1) that the Petition is free of false material allegations; and (2) that the requested name change is not sought for an illegal or fraudulent purpose. A change of name upon marriage, dissolution, or divorce meets these requirements.

Must the child agree to the name change? No, but the court may consider the wishes of a child old enough to express their wishes in considering whether to grant the Petition.

Must the parent(s) of the minor agree to the name change? There is no specific requirement that the parent(s) agree to the name change. Their objections could be considered by the court in determining whether the Petition should be granted.

Hope it Helps U!!

Requirements for Name Change Order:

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To the OP:
That a birth certificate is a legal document. Therefore it requires a court of law to amend it. Parents have rights and a child's name generally cannot be changed without both parent's permission.

The good news is that, one can use any name they want as long as there is no intent to defraud. If you explain to the school, that while the child's legal name is Doe, you want the child to be addressed by your family name of Smith. Generally the schools will comply.

But if you want to legally change the name, you have to get permission from the father's or show a good faith effort that you tried to.

Have you thought of having your new partner adopt them?

As scott pointed out you can ask that they be called whatever you want them to be called. The only difference is that on legal or "official" papers and documents their legal name will have to be used. That is a lot easier than trying to track down the father(s) especially if the father(s) then deny your request.