2 models updated from 1 form view using rails 3.2.1

grrr.rb

### Setup

mkdir 2_models_1_view
rails new 2_models_1_view
rails g scaffold Parent name:string age:integer
rails g scaffold Children toy:string hair:string eyes:string parent_id:integer
rake db:migrate



### models/parents.rb
class Parent < ActiveRecord::Base
  attr_accessible :name, :age, :children_attributes
  has_many :children

  accepts_nested_attributes_for :children, :allow_destroy => true
end

### models/children.rb
class Child < ActiveRecord::Base
  belongs_to :parent
end


### parents_controller.rb
# GET /parents/new
# GET /parents/new.json
def new
  @parent = Parent.new
  @parent.children.build

  respond_to do |format|
    format.html # new.html.erb
    format.json { render json: @parent }
  end
end


### views/parents/_form.html.erb
<%= form_for(@parent) do |f| %>
  <% if @parent.errors.any? %>
    <div id="error_explanation">
      <h2><%= pluralize(@parent.errors.count, "error") %> prohibited this parent from being saved:</h2>

      <ul>
      <% @parent.errors.full_messages.each do |msg| %>
        <li><%= msg %></li>
      <% end %>
      </ul>
    </div>
  <% end %>

  <div class="field">
    <%= f.label :name %><br />
    <%= f.text_field :name %>
  </div>
  <div class="field">
    <%= f.label :age %><br />
    <%= f.number_field :age %>
  </div>

  <%= f.fields_for :children do |xxx| %>
	<hr />
  	<%= xxx.label :toy, "toy" %><br />
  	<%= xxx.text_area :toy %><br />
  <% end %>

  <div class="actions">
    <%= f.submit %>
  </div>
<% end %>