Finding parent process ID on Windows
C:\> wmic process get processid,parentprocessid,executablepath|find "process id goes here"
Based on joslinm's solution in the question, here's a snippet of how to use this in a batch script:
set PID=<this is the child process ID>
for /f "usebackq tokens=2 delims==" %%a in (`wmic process where ^(processid^=%PID%^) get parentprocessid /value`) do (
set PARENT_PID=%%a
)