If you want to see the total of the subtasks time displayed on the parent you have to enable the field Time Tracking on the parent which, in turn, then adds Log Work to the menu. We want to prevent people from logging time on the parent in error, it happens quite regularly and it is not an easy error to detect so the impact is often some spending quite a few minutes trying to sort out the time as it then start affecting the burn-down.

We have the policy that time is only legged in subtasks which works very well apart from this recurring error that people make logging to the parent instead of the subtask