Dealing with young children putting multiple fingers on screen

I am making a simple drag and drop game for a very young audience for iPad only

In testing, I have noticed the kids often rest their thumb or other fingers on the screen whilst attempting to drag one of the draggable items. The placement of multiple fingers on the screen stops the dragging functionality from working.

I therefore would like to know how others deal with this. I am using Flash CS6 and Air 3.4.

My code that deals with the dragging and dropping is as follows:

<code>

function initDragger(mc:MovieClip):void

{

          mc.addEventListener(MouseEvent.MOUSE_DOWN, function (e:MouseEvent):void

          {

                    e.currentTarget.startDrag();

                    objGame.currentDraggingObject = e.currentTarget;

                    stage.addEventListener(MouseEvent.MOUSE_UP, dropObject);

          });

}

function dropObject(e:MouseEvent):void {

          objGame.currentDraggingObject.stopDrag();

          checkDropPosition(e.currentTarget);

});

</code>