If you want to load wordpress child theme css after parent theme cssAdd the priority. Here 99 is high, so it will likely be last but some plugins may add css at a higher priority, though it’s rare.
wp_enqueue_style( 'bootstrap', get_template_directory_uri() . '/../your-child-theme/plugins/bootstrap/css/bootstrap.min.css' );
add_action( 'wp_enqueue_scripts', 'my_theme_enqueue_styles', 99 );
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