Property 'foo' is protected and only accesible through an instance of class 'Foo' (in instances of Foo)

I have the following code in my Typescript. But it reports the following error in the child._moveDeltaX(delta) line:

ERROR: Property '_moveDeltaX' is protected and only accesible 
       through an instance of class 'Container'   
INFO:  (method) Drawable._moveDeltaX( delta:number):void

The code is the folowing:

class Drawable {

    private _x:number = 0;

    constructor() {}

    /**
     * Moves the instance a delta X number of pixels
     */
    protected _moveDeltaX( delta:number):void {
        this._x += delta;
    }
}

class Container extends Drawable {
    // List of childrens of the Container object 
    private childs:Array<Drawable> = [];

    constructor(){ super();}

    protected _moveDeltaX( delta:number ):void {
        super._moveDeltaX(delta);
        this.childs.forEach( child => {
            // ERROR: Property '_moveDeltaX' is protected and only accesible
            //        through an instance of class 'Container'
            // INFO:  (method) Drawable._moveDeltaX( delta:number):void
            child._moveDeltaX(delta);
        });
    }
}

What do I have wrong? I thought that you can access to a protected method. In other lenguajes this code would work without problem.

You "childs" object is not in in visibility of the inherited object. You just made a new instance that cannot access the protected method. You can access the protected methods using super, but not for other instances.

This would fail in c# as well (I think).