The "include sub-tasks" option there is only intended to allow you to sum the time tracking of all the subtasks into the parent issue. That checkbox won't change the estimate for the parent issue, only the way the time tracking is displayed for the parent issue. The time tracking and estimates are actually separate entities.
Configuring Estimations and Time Tracking explains this more.
When using the Burndown Chart, note that sub-task behavior can vary, depending on whether or not remaining estimate and time spent is enabled for your board.
So the way subtasks affect the burndown chart does depend on what value you have in the Board -> Configure Board -> Estimates.
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