Chad,
The easiest way to do this is to show all of the Work Items, expose the 'Leaf Tasks Progress Reporting Policy' field to the work plan as a column. Activate the first one and then do a copy/Paste to the others.
You can also do a separate Data Loader upload that will update all of these items with this setting but that will likely take longer. In the future, you can add that field and desired value (i.e. TRUE for Enabled) to any Work Item level Uploads going forward.
Sincerely,
Boris