On the iPhone app, when a task contains subtasks, that notification contained inside the button that you click on to view the subtasks is at the bottom of the Task detail display.
I recommend that it be moved to the top of the list. Often I know that there are subtasks, but have to scroll down the screen to see and action the button. And, there are times when I forget that a task has subtasks, and may not scroll down. Putting that button at the top makes it very obvious that a task has subtasks, and is more ergonomic and contributes to a better "flow" when working in the app.