I believe that is good.  I'll commit it after the 3.2 release has been cut (we're in release candidate release blocker only lockdown right now).

Looking at ForkingMixIn.collect_children() there appears to be another buglet: it loops over self.active_children and calls self.active_children.remove(pid).  This modification of the list while looping over it will cause it to skip the next item in the list.  For every child waited on successfully, it skips checking one of the others.