Targeting mc's within externally loaded .swf--I'm just not getting it

I have an .swf which I call into a loader identified as “level_”. I want to do a hitTest between a MovieClip in the main file and a MovieClip on level_'s Stage. In AS 2.0, the path would’ve been: this.level_.wall0

I get this error: [FONT=&quot][FONT=Verdana][SIZE=2]1119: Access of possibly undefined property wall through a reference with static type flash.display:Loader.[/SIZE][/FONT][/FONT]

Tracing the .numChildren of the loaded .swf reveals that it has zero children. Within that .swf wall0 and the other MovieClips are instances dragged from the Library and given names. So what am I missing? Is the problem that wall0 hasn’t been properly added as a child in the externally loaded .swf? Or is it something I need to resolve in the main .fla?

Any assistance will be much appreciated!