Now the children page template (event.page.entry) has the option not to sort/position page. But when I change the status of children from parent blueprint page I still have an option to position it (“Bitte wählen Sie eine Position aus”):
The only technical difference between “listed” and “unlisted” statuses of pages is the presence of the sorting number. You could therefore allow only “draft” and “unlisted” for the event pages (instead of the current “draft” and “listed”).
Please delete the thread, I’ve made pretty stupid mistake where to put “num:” value. Now everything works as intended. The error was behind the keyboard.