Cannot create an addEventListener to movieclip in frame 3 (HTML5 Canvas)

On the main timeline, I have different interfaces to a game I am creating. They are all placed on different keyframes.

On frame 3 (which is a keyframe) of main timeline, I have 9 different buttons. On this frame, I have code to create EventListeners for these buttons, but I receive the error of "undefined".

I believe that the code is being executed before the buttons are actually created on the canvas.

Is there an "on loaded" or "on complete" event that I can assign to the frame, so that I can execute code once every object in the frame is created on the canvas?

Thanks for your help.