'Returns list of friendly titles for our selected children only; without
thi, all possible children\'s titles would be seen in the sequence bar in
the LMS.
This overwrites the get_content_titles method included in x_module by default.'

def get_content_titles(self):

    titles = []
    for child in self._xmodule.get_child_descriptors():
        titles.extend(child.get_content_titles())
    return titles
