I have 3 kids from my long time lived -in partner ages 13,14 & 19. Since birth they're using my maiden name. Now that me and my long time live-in partner married, I want my kids to use their dad's last name which I'm using it since we got married. My question is, what form do I file and where to file. Can I do this by myself and how much will it cost me? I live in las vegas and I don't even know where place do I go to do this. Thank you and GOD bless.

Is he on their birth certificate? If so, all you should need to do is show the marriage license to anyplace (schools, etc.) and tell them to use the father's last name now.