get_term_children specific no id

Question

Based on your comment:

the problem is that I am in this situation category-> training->
basketball, according to the archive page taxonomy basketball, I would
like to let all the training children out and I would not do it with
the id

What you’re actually trying to do is get all terms that are ‘siblings’ of the current term i.e. terms with the same parent.

You can do this by using the current term’s parent ID combined with get_terms(), like this:

$current_term = get_queried_object();
$siblings     = get_terms(
    [
        'taxonomy' => $current_term->taxonomy,
        'parent'   => $current_term->parent,
    ]
);

echo '<ul>';

foreach ( $siblings as $sibling ) {
    echo '<li><a href="' . get_term_link( $sibling ) . '">' . $sibling->name . '</a></li>';
}

echo '</ul>';

Note that by using get_terms(), rather than get_term_children(), I avoid the need to use get_term_by().

You can simplify this code even further by using wp_list_categories() to output the HTML for a list:

$current_term = get_queried_object();

wp_list_categories(
    [
        'taxonomy' => $current_term->taxonomy,
        'parent'   => $current_term->parent,
    ]
);