To see a working sample of the application go to : http://syncsample.apphb.com Open the url in two browser windows then drag and drop the tasks and see them sync'd in the other browser.
The key points to take away from this sample is that knockoutjs deals with childcollections in a very specific way. Each child collection needs to be wrapped by a knockout object in order to bind your child arrays to the ui templates. So, when you send an object that has child arrays down to the client using singalR, you need to map from the server types, to an identical structure that has the child arrays wrapped with the knockout observable array object.