Load swf into an instance

In the first frame of my movie, I want to load a swf into 'cwgmap' mc instance, which is inside 'thumbs' mc instance. I am attempting (with no joy!)

thumbs.cwgmap.loadMovie("2014_map/thumbs.swf");

Any ideas how I can achieve this? The action must be in the first frame of the movie - not attached to the mc itself. Driving me mad!

many thanks