Hmm. Problem solved, although I don’t know what made the difference.
Sometime within the last 5 hrs., the option appeared again.
I admit to nOOb-status in here, and want to understand if I caused this myself. So I was thinking: I have worked with a number of draft pages, and only 5 hrs. ago did I actually publish any of it (and then only the front page). Was that it? You can’t hook draft pages up in a parent/child-relationship?