AS3 check container and addChild if empty

Apologies for the dumbness of this query, but I just can’t get this to work…

I have a button on stage which has a child menu movieclip and that movieclip has three submenu button children.

On each of these 3rd level buttons an event listener draws a new container on the stage and adds a new movieClip holding various info.

This all works nicely, but I cannot work out a way to get an eventListener on the menu buttons to check if the container already exists so I can then stop the button repeating the add container function. So, at the moment you can repeatedly hit any of these menu buttons and they will just continue to add info movieClip children.

I’ve tried some nice Boolean commands that should work, but I think it’s the nesting of the children/relationships that are not allowing me to get this to work.

So, basically for arguments sake, let’s say I only have one of each item… here’s the nesting of children:

[COLOR=Blue]stage.[/COLOR]menu_btn.[COLOR=Green]menu_mc.[/COLOR][COLOR=Red]subMenu_btn[/COLOR] (all exist on the stage)

[COLOR=Blue]stage.[/COLOR]container.[COLOR=Green]info_mc[/COLOR] (created at runtime)

Any help would be greatly appreciated!