Child Theme : function/widgets php file doesn't remplace original

Hi David. The widget is loaded using a function in the parent theme. You need to copy that function to your child theme functions.php file:

function alx_load() {
  // Load theme languages
  load_theme_textdomain( 'hueman', get_template_directory().'/languages' );

  // Load theme options and meta boxes
  load_template( get_template_directory() . '/functions/theme-options.php' );
  load_template( get_template_directory() . '/functions/meta-boxes.php' );

  // Load custom widgets
  load_template( get_template_directory() . '/functions/widgets/alx-tabs.php' );
  load_template( get_template_directory() . '/functions/widgets/alx-video.php' );
  load_template( get_template_directory() . '/functions/widgets/alx-posts.php' );

  // Load custom shortcodes
  load_template( get_template_directory() . '/functions/shortcodes.php' );

  // Load dynamic styles
  load_template( get_template_directory() . '/functions/dynamic-styles.php' );

  // Load TGM plugin activation
  load_template( get_template_directory() . '/functions/class-tgm-plugin-activation.php' );
}

Then change this line:

load_template( get_template_directory() . '/functions/widgets/alx-tabs.php' );

to this to load the widget from your child theme:

load_template( get_stylesheet_directory() . '/functions/widgets/alx-tabs.php' );

More information in the theme documentation.