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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 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