Get all children titles of a page as a link to them

What you put doesn’t make much sense, as it turns a 1 step action, into a 4 step action

Why not just put:

$oferta =  get_page_by_title( 'Oferta' );
$my_query = new WP_Query( array(
    'post_type' => 'page',
    'post_parent' => $oferta->ID
) );