code: function( geometry, pos, angle ){
  
              this._aabb = null;
              this.children.push({
                  g: geometry
                  ,pos: new Physics.vector( pos )
                  ,angle: angle
              });
  
              return this;
          }
docs: CompoundGeometry#addChild( geometry, pos ) -> this
  - geometry (Geometry): The child to add.
  - pos (Physics.vector): The position to add the child at.
  - angle (Number): The rotation angle
  
  Add a child at relative position.