If your ex-wife has kids through adultery and they have your last name are you obligated to pay support for them even though they are not yours?

Were you married at the time the children were born? Is your name on the birth certificates? If you were already divorced and your name is not the birth certificates (and if you were divorced then your name wouldn't on the b.c. without your permission/a court order), then you have no obligation. It doesn't matter that they have your last name. If, however, you were married at the time they were born and your name is on the b.c., that's a different story.In that case, there's a possiability you could still be held legally responsible for them, even if a DNA test proves they're not your biological children. The reason being is that there is a time limit for a man to deny paternity. Once it passes, you're out of luck.The laws do vary from state to state, so I'd suggest you speak with an attorney about it.