date_select in a collection

I have a multi model form with a collection of 'child' objects. When
the form gets posed back the children are all nicely in
child_attributes but the dates are not. I can see from the HTML that
the [] of the other fields gets replaced due to the date field already
being multi parameter.

  <% fields_for "client[child_attributes][]", new_child do |f| %>
    <%= f.text_field 'first_name', "size" => 10 %>
    DOB: <%= f.date_select 'dob', :order =>
[:month, :day, :year], :start_year => Time.now.year - 15, :end_year =>
Time.now.year %><br />
  <% end %>

Thanks in advance for any assistance.

Hugh