The sentinel creates a named pipe, but the parent's end of the pipe is inherited by subsequently created children.  

import multiprocessing,signal,sys
def sproc(x): signal.pause()
for each in range(int(sys.argv[1])):
  multiprocessing.Process(target=sproc, args=(each,)).start()
signal.pause()

Running the above on Linux with varying numbers of child processes (expressed as the argument to the above) and using techniques like "$ sudo ls /proc/NNNN/fd" it is possible to see an ever growing number of pipe connections for subsequent children.