Why can't read properties of list<MapItem> from a Qml map?

PowerNow

Unfortunately the current methode (create dynamically Qml objects in C++) and then add them to the map via addMapItem is slow. The reason is that I always must iterate through all childrens.

C++

QMetaObject::invokeMethod(m_pMapObj, "addPlace", Q_ARG(QVariant, i->id));

Qml

Map {
   id: iMap
...

function addPlace(placeIdx) {
  if (iMap.children) {
      for (var child in iMap.children) {
          var currentPlace = iMap.children[child];

         if (currentPlace.idx === placeIdx) {
              iMap.addMapItem(currentPlace);
             break;
          }
      }
  }
}
}

This works, but too slow. Now I found mapItems

mapItems : list<MapItem>

I can iterate through the MapQuickItem's but have no access to any property.

Qml

for (var chd in iMap.mapItems) {
      var cP = iMap.mapItems[chd];

      console.log("name " + cP.sourceItem.objectname);
}

Output

qml: name undefined

Does maybe anyone know what I'doing wrong here? Thxs...