A better form to edit multiple child records. Created for https://github.com/gregbell/active_admin/issues/1097

gistfile1.erb

<%= semantic_form_for @parent do |a| %>

  <%= a.inputs "Family Details" do %>
      <%= a.input :name  %>
      <%= a.input :user %>
      <%= a.input :region %>
  <% end %>

  <%= a.inputs "Children" do %>
    <table>
      <tr>
        <th>First Name</th>
        <th>Last Name</th>
        <th>Age</th>
        <th>Gender</th>
      </tr>

      <%= a.semantic_fields_for :children do |b| %>
        <tr>
          <td><%= b.input :first_name, :label => false %></td>
          <td><%= b.input :last_name, :label => false %></td>
          <td><%= b.input :age, :label => false %></td>
          <td><%= b.input :gender, :label => false %></td>
          <td><%= link_to "Remove", "#", onclick: "
              if (confirm('Are you sure you want to delete this?\
              \\nIt will be permanently deleted!')) {
                $.ajax({url: '/children/#{b.object.id}', type: 'DELETE'});
                $(this).closest('tr').remove(); return false;
              }", :class => "button" %></td>
        </tr>
      <% end %>

      <% js = a.semantic_fields_for :children, Child.new do |c| %>
        <tr>
          <td><%= c.input :first_name, :label => false %></td>
          <td><%= c.input :last_name, :label => false %></td>
          <td><%= c.input :age, :label => false %></td>
          <td><%= c.input :gender, :label => false %></td>
          <td><%= link_to "Remove", "#", :onclick => "$(this).closest('tr').remove(); return false;", :class => "button" %></td>
        </tr>
      <% end %>

    </table>

    <span class="add-child">
      <% js = escape_javascript(js) %>
      <%= link_to I18n.t('active_admin.has_many_new',
          model: @child.to_s.singularize.titlecase), "#",
          onclick: "$('table.children tr').last().after(
                      '#{js}'.replace(/[0-9]+(?=[\\\]_])/g, new Date().getTime())
                    ); return false;",
          class: "button" %>
    </span>
  <% end %>

  <%= a.actions do %>
    <%= a.action :submit %>
    <li class="cancel"><%= link_to "Cancel", parent %></li>
  <% end %>

<% end %>

You need to change the first line to:

<%= semantic_form_for [:admin, @parent] do |a| %>

and likewise in the actions block on the bottom:

<li class="cancel"><%= link_to "Cancel", [:admin, @parent] %></li>

thanks for this, it's a lot nicer. I found another thing for me to make it working.
It didn't do anything when clicking on "add a new child". just add a class to the table:

 <%= a.inputs "Children" do %>
    <table class="children">
      <tr>

so that it get found when calling in javascipt here:

<%= link_to I18n.t('active_admin.has_many_new',
          model: @child.to_s.singularize.titlecase), "#",
          onclick: "$('table.children tr').last().after(
                      '#{js}'.replace(/[0-9]+(?=[\\\]_])/g, new Date().getTime())
                    ); return false;",
          class: "button" %>
    </span>