// Any DisplayObjectContainer (such as a MovieClip or the stage) has a method called 
// getObjectsUnderPoint that returns an array of display objects under that point. It takes a // Point object as an argument.

var myObjects: Array = stage.getObjectsUnderPoint(new Point(5, 5));

// If you are using it in a class don't forget to import flash.geom.Point;

This can be a point you define or a mouse cursor etc.

Get DisplayObject under Point

ActionScript 3