How to get page id in function.php file?

Question

WordPress

Hello. Tell me, is it possible to dynamically get the page id in the function.php file?

add_action('wp_ajax_nopriv_ajax_search', 'ajax_search');
add_action('wp_ajax_ajax_search', 'ajax_search');
function ajax_search()
{
    
    $postID = get_queried_object_id();
    $args = array(
        'post_type'      => 'lessonone', // Тип записи: post, page, кастомный тип записи
        'post_status'    => 'publish',
        'order'          => 'DESC',
        'orderby'        => 'date',
        'post_parent' => $postID,
        's'              => $_POST['term'],
        'posts_per_page' => -1
    );
    $query = new WP_Query($args);
    if ($query->have_posts()) {
        while ($query->have_posts()) {
            $query->the_post();?>
            <li class="ajax-search__item">
                <a href="<?php the_permalink(); ?>" class="ajax-search__link"><?php the_title(); ?></a>
                <div class="ajax-search__excerpt"><?php the_excerpt(); ?></div>
            </li>
        <?php }
    } else { ?>
        <li class="ajax-search__item">
            <div class="ajax-search__not-found">Ничего не найдено</div>
        </li>
    <?php }
    exit;
}

The bottom line is that the search only searches for child pages of the current page