If what Jerry has mentioned above doesn't work, or using a wire coat hanger, or paper clip unraveled, I would just send it to a pro to resolve:
Tim West comes to mind:
http://www.jhlowe.com/tobacco_pipe_repairs.htm
You could simply give him a call to discuss prior to mailing the pipe to him. Don't know what the quality of the churchwarden is, but it may come down to replacing the stem period.
Hopefully, your son will use "churchwarden" pipe cleaners next time, or if he did, a little patients goes a long way in cleaning a churchwarden stem (and using a bit of whiskey/bourbon usually helps too)
That's my
Good Luck brother...