If you have activated the plugin, access a confluence page that has one or more child pages.

Now you can access the “Delete page tree” function via the “Tools” menu.Selection_001 This takes you to a short overview. That lists which pages are going to be deleted. In addition to this it shows pages that are not going to be deleted because of set permissions.Selection_002

After verifying that this is what you want to delete, press the delete button on the bottom of the page.

You can get the plugin at https://marketplace.atlassian.com/plugins/at.rumpelcoder.confluence.deletepagetree