CaractType.php

$builder->add('selected', 'checkbox', array('required' => false,));

ConceptType.php

        $builder->add('caracts', 'collection', array('type' => 'TrouveTout_Caract',
                                                     'label' => ' ',
                                                     'allow_add' => true,
                                                     'allow_delete' => true,
                                                     'by_reference' => false,
                                                     'options' => array('display_type' => 'edit',
                                                                        'parentType' => $parentType)));