vatican city tens thousands people many children serenade pope francis 81st birthday sunday pontiff appeal release catholic nuns kidnap last month nigeria crowd sing happy birthday italian pontiff appear window apostolic palace overlook st. peter square weekly message bless first latin american pope bear jorge mario bergoglio dec. 17 1936 buenos air former cardinal argentine capital become leader world 1.2 billion roman catholics 2013. keep long-standing tradition rome children face pope window hold small statues baby jesus bless statues place home nativity scenes custom still practise many italian families francis often warn excessive materialism holiday season depart address say real christmas remove jesus leave empty feast appeal release six roman catholic nuns kidnap convent town iguoriakhi nigeria last month francis say hop victims kidnappings could home christmas children serenade pope 81st birthday appeal kidnap nuns