General DataSource Question (GeoJson, kml,...)

I am currently using the CesiumWidget, and am creating a real time application which receives in dynamic data in GeoJSON and or KML formats. When the data is received I am calling the appropriate load method loadKML on the KmlDatasource or load on the GeoJsonDataSource. When the promise is resolved from the load operation I am getting the entities out of the Datasource entityCollection. At that point I was trying to add the entities to the scene, but that was not working. I then tried to create primitives out of the entities and add those to the scene. That also did not work. Does anybody know what the entities are in the entityCollection? What is the proper method/function which should be called so they can appear on the scene? I did spent some time looking at the CesiumVierwer code to see how they handle dataSources, but nothing jumped out.

Thanks in advance