Get all children including children of children

        :returns: all children including children of children
        :rtype: list of :class:`Reftrack`
        :raises: None

def get_all_children(self):
        """Get all children including children of children

        :returns: all children including children of children
        :rtype: list of :class:`Reftrack`
        :raises: None
        """
        children = self._children[:]
        oldlen = 0
        newlen = len(children)
        while oldlen != newlen:
            start = oldlen
            oldlen = len(children)
            for i in range(start, len(children)):
                children.extend(children[i]._children)
            newlen = len(children)
        return children