// number_of_children
    $number_of_children = new Zend_Form_Element_Select('number_of_children');
    $number_of_children->setLabel('Number of your children below the ags of 21')
                       ->setOptions(array('onChange' => 'submit();'))
                       ->setMultiOptions(array('1', '2', '3', '4', '5' ,'6' ,'7', '8'))
                       ->setRequired(true)
                       ->addValidator('NotEmpty', true); 
    
    // text fields for a name for each child
    if ($this->_request->isPost()) {
        // if number_of_children submitted the form, and not the save submit        
        // button then use its value to create name fields
        if ($this->_request->getPost('save') != 'save' && !empty($this->_request->getPost('number_of_children'))) {
            for ($i = 0; $i < $this->_request->getPost('number_of_children'); $i++) {
                // define the field name for this iteration.  the first one will be
                // named child_name_1, then child_name_2, and so on...
                // and add any options, validators, filters, etc...
                $fieldName = new Zend_Form_Element_Text('child_name_' . $i);
                $fieldName->setLabel('Name:')
                          ->setOptions()
                          ->addValidator()
                          ->setRequired()
                          ->addFilter();            
            }
        }
    }