I can designate a parent task ("Check earthing") as dependent on the completion of one or more of its subtasks, but someone who has been assigned the parent task and its subtasks can close the parent task and all of its subtasks with close without a warning and without any of them having been closed (completed).

I am new to Projects. I am correct here? Or have I missed something?

I need to be able to ensure that all subtasks under a parent task are completed before the parent task can be closed.