Are the sub-projects parallel or sequential?
If they are parallel, they can all move forward at once:
* Back to school shopping (project)
* Clothes for Tom
* Computer for Jane
* Dorm stuff for Harry
And so they should all be "active" projects for purposes of the weekly review.
If they are sequential, only one can move forward at a time:
* Build bridge
* Submit bid for bridge construction
* Design bridge
* Collect bids from subcontractors
And so only the current one needs to be active.