ActionScript 3.0 :: AddChild Is Undefined Method

I have four classes -

class Init - intialises some variables, and is the doc Class.
class Street - loads XML data for, say, a number of streets in a particular area
class House - loads in the houses data for one particular street
class DisplayHouse - displays graphics on screen for the houses

This all seems to be working apart from the actual graphical display of objects.In the ouput window I am seeing the results I need to see pertaining the the XML data loaded.The problem is that in House - I have the code :

var new _house = new DisplayHouse();
addChild (_house);

and DisplayHouse is a simple graphics-shape:

var drawHouse:Sprite=new Sprite();
code... to draw house!
addChild(drawHouse);

Now, when I comile, I keep getting this error:

Location: House.as
Description: 1180:call to undefined method addChild
Source: addChild (_house);

House extends sprite and has import Sprite and all that! - infact all the classes have the same imports and extend Sprite!semi-colons are all in right places, there are no typos!I simply cannot understand why addChild is an undefined method in this case!