Projects or Areas?
We have product with several applications like MS Office with Word, Excel, etc.
For more granularity I'd recommend creating a project for each of your "child" apps, so that you can have areas within them.
If one team is responsible for different child apps, using area's will enable people to oversee bugs on different child apps. If typically performed by different people, then using projects helps for oversight.
Adriaan van den Brand
Fog Creek Home