How can I check if a symbol/MC is a child of another symbol/MC?

I'm using Adobe Animate HTML5 Canvas. EaselJS would also apply.

How can I check if a symbol/MC is a child of another symbol/MC?

So a symbol/MC is added as a child of lensParentLeft in the following. I then want to check if it is a child of that parent in a later function:

function onMouseUp(evt){
    var item = evt.currentTarget;
    item.drag = false;
    var pt = item.localToLocal(item.dot.x, item.dot.y, item.LFLensHolder.hitBox);
    if(item.LFLensHolder.hitBox.hitTest(pt.x, pt.y) ){
        item.x = item.LFLensHolder.x;
        item.y = item.LFLensHolder.y;
        item.lensParentLeft.addChild(item);
        }
}

The later function being the following, probably in the if(item.drag) condition statement:

function onMouseMove(evt){
    var item = evt.currentTarget;
    if (item.drag){
        var pt = item.parent.globalToLocal(evt.stageX, evt.stageY);
        item.x = pt.x - item.offset.x;
        item.y = pt.y - item.offset.y;
    }
}

You can use the contains method. It does a recursive parent check up to the stage to find an ancestor.

https://createjs.com/docs/easeljs/classes/Container.html#method_contains

if (someParent.contains(evt.currentTarget)) {
  // Do something
}

Note that contains will also return true if you check a symbol against itself.