A lot of his children find it so weird that he would leave. Given that he just told them that he was having a pleasant conversation with his other selves.

Sevet was very young and naive.

That doesn't sound like a good enough justification!

At that age you are very sure of things that you shouldn't. It's part of growing up.

Sevet is very sure! He is old enough to be sure that he wants to leave.

Alright, alright. They can go inside and try the door. Even if that was not the way which Sevet came from it should work.

Sevet has never been inside a build before, and in other situations he would've been curious about it. Not now. When they reach the door, it opens to somewhere underwater.

Is that the end of the story?

He usually gives them a different answer each time. Usually after a dramatic pause. Sometimes he tells then it is, and it's time to sleep. Sometimes he recounts the tale of when he mets their mother (or other father).