ah. ok then. 0/2 at the moment with these theories -____-

lol, i still think Sokka is the father. Hear me out. Sokka did end up with Suki, but no relationship is perfect. Maybe at some point, they got into a fight a Sokka left for a while. He goes and talks with his good friend Toph for guidence as she tends to have the ability to see things others overlook.

However, he's really made at Suki, one thing leads to another and they end up doing it. Sokka regrets what happened and is no longer mad at Suki. He goes back to her and Toph understands completely.

However, Toph finds out later that she is pregnant. Not wanting to ruin Sokka's reputation since he is on council, she maintains that the father was some one night stand that she will never see again.

I know, right? They may of grew up together, and had a relationship having no idea that they were in fact cousions. Then one day Tenzin was told by Toph which is why he ended it so abruptly.