getNextChild(child) {
		const index = this.getChildren().indexOf(child) - 1;
		if (index >= 0 && index < this.getChildren().length) {
			return this.getChildAt(index);
		}
		return undefined;
	}
Returns the next child within the container or undefined if none
@param {Renderable|Entity|Sprite|Collectable|Trigger|Draggable|DropTarget|NineSliceSprite|ImageLayer|ColorLayer|Light2d|UIBaseElement|UISpriteElement|UITextButton|Text|BitmapText} child - The child object
@returns {Renderable} child