+/**
+ * Kill all children.
+ *
+ * @todo It would be kind of nice to make sure that they are actually
+ * all our children before we kill them, because their pids may have
+ * been recycled by some other process. Perhaps when we wait for a
+ * child, we should remove it from this array. Alternatively we could
+ * perhaps use process groups, but I think that would not work on
+ * ancient Unix versions that don't support them.
+ **/