KML 1       KML 2
$('#test').gmap3(
  { action: 'addKmlLayer',
    url: 'http://gmdesign.org.uk/bb/script/kml/01.kml',
    options:{
      suppressInfoWindows: true
    },
    tag:'chk1'
  },
  { action: 'addKmlLayer',          
    url: 'http://gmdesign.org.uk/bb/script/kml/02.kml',
    options:{
      suppressInfoWindows: true
    },
    tag:'chk2'
  }
);

$('.tools input[type=checkbox]').change(function(){
  var map = $('#test').gmap3('get'),
      kml = $('#test').gmap3({
        action:'get',
        name:'kmllayer',
        tag: $(this).attr('id')
      });
  kml.setMap( $(this).is(':checked') ? map : null );
});