public class KmlLayer : GraphicsLayer
{
  internal GraphicCollection graphics;
  internal List<KmlLayer> ChildLayers;

  public new GraphicCollection Graphics
  {
    get 
    {
      GraphicCollection gc = new GraphicCollection();
      foreach(Graphic g in this.graphics)
        gc.Add(g);
      foreach(KmlLayer kl in this.ChildLayers)
        foreach(Graphic g in kl.Graphics)
          gc.Add(g);
      return gc;
    }
    set { return this.graphics; }
  }
.
.
.
}

foreach(KmlLayer kl in this.ChildLayers)
    foreach(Graphic g in kl.Graphics)
        if(!this.Graphics.Contains(g))
            this.Graphics.Add(g);

//also note that GraphicsLayer.Graphics is settable as well if you prefer modifying the entire instance itself

<Placemark>
<name>SKW6078</name>
<Style id='fbstyle80787715'>
<IconStyle>
<heading>0</heading>
<Icon><href>root://icons/palette-2.png</href><y>0</y><w>32</w><h>32</h></Icon
></IconStyle>
</Style>
<description>...</description>
<styleUrl>#fbstyle80787715</styleUrl>
<Point>
<extrude>1</extrude><altitudeMode>absolute</altitudeMode>
<coordinates>
-118.19,33.9655555555556,10668
</coordinates>
</Point>
</Placemark>

<Placemark><styleUrl>#fbpaths</styleUrl>
<LineString>
<tessellate>0</tessellate>
<altitudeMode>absolute</altitudeMode>
<coordinates>
-118.19,33.9655555555556,10668 ... -118.331666666667,33.9527777777778,11667
</coordinates>
</LineString>
</Placemark>