MVC2 RTM - model binding complex objects using Entity Framework

Question

I am new to MVC, and am really struggling with what I seems like it should be a very common scenario. I'm using MVC2 RTM, and the Entity Framework for my model objects.

What I have working:

An edit view for a parent object that contains a collection of child objects. The form displays all the editable fields for the parent, and iterates through and displays all editable fields for all the associated child objects (in the same view). I am able to successfully handle the edit action in my controller, but run into issues when I try to bind values in the form collection to the EF model objects.

The problem:

In my controller function, when I call TryUpdateModel and pass the parent object, I get the following error:

"The EntityCollection has already been initialized. The InitializeRelatedCollection method should only be called to initialize a new EntityCollection during deserialization of an object graph."

I have seen a lot of other posts from people struggling with similar issues, but have not found a solution. Is this not possible without building a custom model binder? If anyone has a working example, I would greatly appreciate it. For some reason, I am able to iterate through the child collection and successfully execute TryUpdateModel on the child objects, but when I call it on the parent, the error above is thrown. Ideally I'd like to call it once for the parent, and have the whole object tree update from the form.

Here's the controller code:

[AcceptVerbs(HttpVerbs.Post)]
public ActionResult Edit(int id, FormCollection formValues)
        {
            EFEntities ef = new EFEntities();
            ParentObject parent = ef.ParentObjects.SingleOrDefault(p => p.ID == id);

            if (ModelState.IsValid)
            {
                int i = 0;
                foreach (child in parent.ChildObjects)
                {
                    //this works fine
                    TryUpdateModel(child, "ChildObjects[" + i + "]"); 
                    i++;
                }

                //this blows up
                if (TryUpdateModel(parent)) 
                {                    
                    ef.SaveChanges();
                    return RedirectToAction("Details", new { id = parent.ID });
                }
            }
            return View(parent);
        }