Does renderer.bounds of Parent GameObject include all children meshes that are rendered?

Does renderer.bounds of Parent GameObject include all children meshes that are rendered?

As in, will the parent renderer.bounds be equal to the sum of all the children renderer.bounds

Do you mean if there are sub meshes - then yes, if you mean things which appear as a hierarchy in the scene then no. If you want to get the bounds of an item and its children:

   Bounds bounds = renderer.bounds;
   foreach(var r in GetComponentsInChildren<Renderer>())
   {
         bounds.Encapsulate(r.bounds);
   }