Profile: garyF-3

add_action( 'save_post', 'auto_set', 100, 3 );
function auto_set( $post_id, $post, $update ) {
  if( $post->post_status == 'publish' && $post->post_type =='child-post-type-slug' ) {
    $parent_id = toolset_get_related_post( $post_id, 'post-relationship-slug' , 'parent', array() );
    $field_value = get_post_meta( $parent_id, 'wpcf-custom-field-slug', true );
    update_post_meta( $post_id, 'wpcf-custom-field-slug', $field_value );
  } 
}