Rails: Autocreate associated records as soon as parent record is saved

I'm trying to automatically create records in a child table as soon as a parent record is saved but I'm stuck and need a help how to do this.

So my table hierarchy of the Orgs is like Org->Brand->Restaurant (eg. Americana(Org) -> KFC(Brand) ->San Francisco(Restaurant)).

A Brand has many menus and Menu belongs to a Brand. Now I want to cascade menu for each Restaurant from the Brand's menu because I want to be manage price by the Restaurant. In order to do that, I created a 'local_menus' table which contains restaurant_id and menu_id so that I don't have to duplicate some data and changes in the local_menus will not be affected to its parent.

The question is how do I auto create records in 'local_menus' as soon as a parent menu is created. To be more specific, when I create a menuA, the same menu needs to be created automatically for all the restaurants under the brand. Appreciate your support.

MODELS:

class LocalMenu < ActiveRecord::Base
  belongs_to :restaurant
  belongs_to :menu
end

class Menu < ActiveRecord::Base
    has_many :local_menus
    belongs_to :brand
end

class Restaurant < ActiveRecord::Base
    has_many :menus, through: :local_menus
end

TABLES:

local_menus
    t.integer  "restaurant_id",  limit: 4
    t.integer  "menu_id",        limit: 4
    t.boolean  "active_status",    limit: 1
    t.boolean  "instock_status", limit: 1
    t.integer  "price",          limit: 4


menus
    t.integer  "restaurant_id",      limit: 4
    t.string   "name",               limit: 255
    t.integer  "price",              limit: 4
    t.integer  "brand_id",           limit: 4
    t.integer  "category_id",        limit: 4
    t.text     "description",        limit: 65535
    t.boolean  "active_status",      limit: 1
    t.date     "start_date"
    t.date     "end_date"

restaurants
    t.string   "name",          limit: 255
    t.string   "name_kana",     limit: 255
    t.integer  "price",         limit: 4
    t.boolean  "active_status", limit: 1
    t.integer  "brand_id",      limit: 4

via Chebli Mohamed