Route failing using STI - ruby-on-rails

Question

First SO post, but I've read so many. I'm new to Rails and building first site since studying Hartl's RailsTutorial.
My issue is routing using STI. I believe the routes are set up correctly, but the subclass Kid doesn't find a "show" route.
Class inheritance using STI
class User < ActiveRecord::Base
class Kid < User
Kid Controller
def show
#kid = Kid.find(params[:id])
end
User Controller create
def create
#user = User.new(params[:user])
if #user.save
flash[:success] = "Welcome to kidtunes!"
if (#user.type = "Kid")
***redirect_to #kid***
else
redirect_to #parent
end
else
render 'new'
end
routes.rb
resources :users, :kids, :parents
root to: 'static_pages#home'
match '/help', to: 'static_pages#help'
match '/contact', to: 'static_pages#contact'
match '/signup', to: 'users#new'
Results in:
kids_new GET /kids/new(.:format) kids#new
users GET /users(.:format) users#index
POST /users(.:format) users#create
new_user GET /users/new(.:format) users#new
edit_user GET /users/:id/edit(.:format) users#edit
user GET /users/:id(.:format) users#show
PUT /users/:id(.:format) users#update
DELETE /users/:id(.:format) users#destroy
kids GET /kids(.:format) kids#index
POST /kids(.:format) kids#create
new_kid GET /kids/new(.:format) kids#new
edit_kid GET /kids/:id/edit(.:format) kids#edit
kid GET /kids/:id(.:format) kids#show
PUT /kids/:id(.:format) kids#update
DELETE /kids/:id(.:format) kids#destroy
parents GET /parents(.:format) parents#index
POST /parents(.:format) parents#create
new_parent GET /parents/new(.:format) parents#new
edit_parent GET /parents/:id/edit(.:format) parents#edit
parent GET /parents/:id(.:format) parents#show
PUT /parents/:id(.:format) parents#update
DELETE /parents/:id(.:format) parents#destroy
root / static_pages#home
help /help(.:format) static_pages#help
contact /contact(.:format) static_pages#contact
signup /signup(.:format) users#new
Error
I get the following on redirect_to #kid
ActionController::ActionControllerError (Cannot redirect to nil!):
app/controllers/users_controller.rb:16:in `create'
I feel like I've checked everything I can check, but I'm still missing something. #kid should properly redirect to the kids#show route. I'm not sure if I have a poorly crafted single table inheritance or a basic routing issue.
thanks in advance.
-John
Form
This form is used in users/new.html.erb and it creates the User.
<div class="row">
<div class="span5 offset2">
<%= form_for(#user) do |f| %>
<%= render 'shared/error_messages' %>
<%= f.label :fname, "First Name" %>
<%= f.text_field :fname %>
<%= f.label :lname, "Last Name" %>
<%= f.text_field :lname %>
<%= f.label :email %>
<%= f.text_field :email %>
<%= f.label :type, "Are you a Kid or Parent?" %>
<%= f.select :type, [['Kid','Kid'],['Parent','Parent']] %>
<%= f.label :password %>
<%= f.password_field :password %>
<%= f.label :password_confirmation, "Confirmation" %>
<%= f.password_field :password_confirmation %>
<%= f.submit "Create my account", class: "btn btn-large btn-primary" %>
<% end %>

Answer 1

Have you defined/assigned values to the #kid or #parent variables? If not, they will be nil, and you'll get the cannot redirect to nil error you've included in your question.
Please include the full code for the create action. Otherwise we're left to trust (rather than read for ourselves) precisely what's happening in the redirect.
Your redirects might also need some work. For example, you could do:
if (#user.is_a? Kid)
redirect_to kid_path(#user)
else
redirect_to parent_path(#user)
end
...or something very similar to that.

Answer 2

First thing I noticed is that you're using = instead of ==:
if (#user.type = "Kid")
I think it's nicer to test it like that:
if #user.is_a? Kid
Can you show us how you set #kid and #parent?