Hi Kasey!
The answer by GerdW is perfectly correct, but it makes it where every time that specific subVI is called, the front panel will pop up. If you want to make it a per-instance occurrence (as opposed to a subVI property), you can right-click on the subVI in the top-level VI's block diagram and choose SubVI Node Setup->"Show Front Panel when Called" & "Close afterwards if originally closed"
Hope this helps!
Travis H.
National Instruments
Travis H.
LabVIEW R&D
National Instruments