This is how the original category template links to content-grid.php (I'm only showing the relevant code):

echo '<div class="row">';
while ( have_posts() ) : the_post();
$count++;
get_template_part( 'template-parts/content-grid' );
if ( $count % 2 == 0 ) {
echo '</div>';

In my customized template I've changed the standard loop to a "foreach" loop and link to the same file like this:

echo '<div class="row">';
foreach ( $child_categories as $child ){
 $count++;
get_template_part( 'template-parts/content-grid' );
if ( $count % 2 == 0 ) {
echo '</div>';

Is there any reason why this shouldn't work?

This is the original category template:

<?php
/**
 * The template for displaying category archive pages.
 *
 * @link https://codex.wordpress.org/Template_Hierarchy
 *
 * @package Codilight_Lite
 */

get_header(); ?>
    <div id="content" class="site-content container <?php echo codilight_lite_sidebar_position(); ?>">
        <div class="content-inside">
            <div id="primary" class="content-area">
                <main id="main" class="site-main" role="main">

                <?php
                if ( have_posts() ) : $count = 0; ?>

                    <header class="page-header">
                        <?php
                            the_archive_title( '<h1 class="page-title">', '</h1>' );
                            the_archive_description( '<div class="taxonomy-description">', '</div>' );
                        ?>
                    </header><!-- .page-header -->

                    <?php
                    $layout_archive_posts = get_theme_mod( 'layout_archive_posts', 'grid' );
                    if ( $layout_archive_posts == 'grid' ) {
                        echo '<div class="block1 block1_grid">';
                        echo '<div class="row">';
                            while ( have_posts() ) : the_post();
                            $count++;
                                get_template_part( 'template-parts/content-grid' );
                            if ( $count % 2 == 0 ) {
                                echo '</div>';
                                echo '<div class="row">';
                            }
                            endwhile;
                        echo '</div>';
                        echo '</div>';
                        codilight_lite_custom_paginate();

                    } else {
                        echo '<div class="block1 block1_list">';
                            while ( have_posts() ) : the_post();
                            get_template_part( 'template-parts/content-list' );
                            endwhile;
                        codilight_lite_custom_paginate();
                        echo '</div>';
                    }
                    ?>

                <?php else : ?>

                    <?php get_template_part( 'template-parts/content', 'none' ); ?>

                <?php endif; ?>

                </main><!-- #main -->
            </div><!-- #primary -->

<?php get_sidebar(); ?>
<?php get_footer(); ?>

...and this is the content-grid.php template file:

<?php
/**
 * Template part for displaying posts with grid style.
 *
 * @link https://codex.wordpress.org/Template_Hierarchy
 *
 * @package Codilight_Lite
 */

?>

<article id="post-<?php the_ID(); ?>" <?php post_class( 'col-md-6 col-sm-12' ); ?>>
    <div class="entry-thumb">
        <a href="<?php echo esc_url( get_permalink() ); ?>" title="<?php the_title(); ?>">
            <?php
            if ( has_post_thumbnail( ) ) {
                the_post_thumbnail( 'codilight_lite_block_2_medium' );
            } else {
                echo '<img alt="'. esc_html( get_the_title() ) .'" src="'. esc_url( get_template_directory_uri() . '/assets/images/blank325_170.png' ) .'">';
            }
            ?>
        </a>
        <?php
        $category = get_the_category();
        if($category[0]){
            echo '<a class="entry-category" href="'.get_category_link($category[0]->term_id ).'">'.$category[0]->cat_name.'</a>';
        }
        ?>
    </div>
    <div class="entry-detail">
        <header class="entry-header">
            <?php the_title( sprintf( '<h2 class="entry-title"><a href="%s" rel="bookmark">', esc_url( get_permalink() ) ), '</a></h2>' ); ?>
            <?php if ( 'post' === get_post_type() ) codilight_lite_meta_1();?>
        </header><!-- .entry-header -->

        <div class="entry-excerpt">
            <?php echo codilight_lite_excerpt(120); ?>
        </div><!-- .entry-content -->
    </div>
</article><!-- #post-## -->

...and now for the customized category template file:

<?php
/**
 * Category Template: Custom
 */

get_header(); ?>
    <div id="content" class="site-content container <?php echo codilight_lite_sidebar_position(); ?>">
        <div class="content-inside">
            <div id="primary" class="content-area">
                <main id="main" class="site-main" role="main">
<?php 
        $cat = get_category( get_query_var( 'cat' ) );
        $cat_id = $cat->cat_ID;
        $child_categories=get_categories(
        array( 
        'parent' => $cat_id,
        // Uncomment the below line if you want empty category to appear on the list. 
        // 'hide_empty'   => 0
    )
); 
        if (!empty($child_categories)) : $count = 0; ?>
                    
                    <header class="page-header">
                        <?php
                            the_archive_title( '<h1 class="page-title">', '</h1>' );
                            the_archive_description( '<div class="taxonomy-description">', '</div>' );
                        ?>
                    </header><!-- .page-header -->

                    <?php
                        echo '<div class="block1 block1_grid">';
                        echo '<div class="row">';
                    
                    foreach ( $child_categories as $child ){ $count++;
                    get_template_part( 'template-parts/content-grid' );
                                
                    if ( $count % 2 == 0 ) {
                                echo '</div>';
                                echo '<div class="row">';
                    }
                    }
                        echo '</div>';
                        echo '</div>';
                    ?>

                <?php else : ?>

                    <?php get_template_part( 'template-parts/content', 'none' ); ?>

                <?php endif; ?>

                </main><!-- #main -->
            </div><!-- #primary -->

<?php get_sidebar(); ?>
<?php get_footer(); ?>

...and the customized content-grid.php template file:

<?php
/**
 * Template part for displaying posts with grid style.
 *
 * @link https://codex.wordpress.org/Template_Hierarchy
 *
 * @package Codilight_Lite
 */

?>

<article id="" class="col-md-6 col-sm-12">
    
    <div class="entry-thumb">
    
        <a href="<?php echo get_category_link( $child->cat_ID ); ?>" title="<?php echo $child ->cat_name;?>">
            
    <?php $image_url = z_taxonomy_image_url($child->term_id); ?>
    
        <?php if (!empty($image_url)) : ?>
            <img alt="" src="<?php if (function_exists('z_taxonomy_image_url')) echo z_taxonomy_image_url($child->term_id);?>" />
    
        <?php else: ?>
            <img alt="" src="<?php echo esc_url( get_template_directory_uri() . '/assets/images/blank325_170.png' ) ?>" />

    <?php endif; ?>
    
        </a>
        
    </div>
    
    <div class="entry-detail">
        
        <header class="entry-header">
            
            <h2 class="entry-title"><a href="<?php echo get_category_link( $child->cat_ID ); ?> " rel="bookmark"><?php echo $child ->cat_name;?></a>
            </h2>
            
        </header><!-- .entry-header -->

        <div class="entry-excerpt">
        
            <?php echo $child ->description;?>
        
        </div><!-- .entry-content -->
    
    </div>
    
</article><!-- #post-## -->

...and lastly this is how I put all the code together in the category template file which works:

<?php
/**
 * Category Template: Custom
 */

get_header(); ?>
    <div id="content" class="site-content container <?php echo codilight_lite_sidebar_position(); ?>">
        <div class="content-inside">
            <div id="primary" class="content-area">
                <main id="main" class="site-main" role="main">
<?php 
        $cat = get_category( get_query_var( 'cat' ) );
        $cat_id = $cat->cat_ID;
        $child_categories=get_categories(
        array( 
        'parent' => $cat_id,
        // Uncomment the below line if you want empty category to appear on the list. 
        // 'hide_empty'   => 0
    )
); 
        if (!empty($child_categories)) : $count = 0; ?>
                    
                    <header class="page-header">
                        <?php
                            the_archive_title( '<h1 class="page-title">', '</h1>' );
                            the_archive_description( '<div class="taxonomy-description">', '</div>' );
                        ?>
                    </header><!-- .page-header -->

                    <?php
                        echo '<div class="block1 block1_grid">';
                        echo '<div class="row">';
                    foreach ( $child_categories as $child ) : $count++; ?>
                                <article id="" class="col-md-6 col-sm-12">
    
    <div class="entry-thumb">
        <a href="<?php echo get_category_link( $child->cat_ID ); ?>" title="<?php echo $child ->cat_name;?>">
            
    <?php $image_url = z_taxonomy_image_url($child->term_id); ?>
<?php if (!empty($image_url)) : ?>
    <img alt="" src="<?php if (function_exists('z_taxonomy_image_url')) echo z_taxonomy_image_url($child->term_id);?>" />
    
<?php else: ?>
    <img alt="" src="<?php echo esc_url( get_template_directory_uri() . '/assets/images/blank325_170.png' ) ?>" />

    <?php endif; ?>
    
        </a>
    </div>
    
    <div class="entry-detail">
        <header class="entry-header">
            <h2 class="entry-title"><a href="<?php echo get_category_link( $child->cat_ID ); ?> " rel="bookmark"><?php echo $child ->cat_name;?></a></h2>
        </header><!-- .entry-header -->

        <div class="entry-excerpt">
            <?php echo $child ->description;?>
        </div><!-- .entry-content -->
    </div>
</article><!-- #post-## -->

<?php ?>
                                
                <?php   if ( $count % 2 == 0 ) {
                                echo '</div>';
                                echo '<div class="row">';
                    }
                    endforeach;
                        echo '</div>';
                        echo '</div>';
                    ?>

                <?php else : ?>

                    <?php get_template_part( 'template-parts/content', 'none' ); ?>

                <?php endif; ?>

                </main><!-- #main -->
            </div><!-- #primary -->

<?php get_sidebar(); ?>
<?php get_footer(); ?>

I'm customizing my theme's category template to display the current category's child categories instead of the posts from that category.

The category template links to another template file (content-grid.php) which generates the dynamic post/category content.

The only way I can get it to work is by including all the code on the category template.

This is how the original category template links to content-grid.php (I'm only showing the relevant code):

echo '<div class="row">';
while ( have_posts() ) : the_post();
$count++;
get_template_part( 'template-parts/content-grid' );
if ( $count % 2 == 0 ) {
echo '</div>';

In my customized template I've changed the standard loop to a "foreach" loop and link to the same file like this:

echo '<div class="row">';
foreach ( $child_categories as $child ){
$count++;
get_template_part( 'template-parts/content-grid' );
if ( $count % 2 == 0 ) {
echo '</div>';

I'm customizing my theme's category template to display the current category's child categories instead of the posts from that category.

The category template links to another template file (content-grid.php) which generates the dynamic post/category content.

The only way I can get it to work is by combining all the code together on the category template.

This is how the original category template links to content-grid.php (I'm only showing the relevant code):

echo '<div class="row">';
while ( have_posts() ) : the_post();
$count++;
get_template_part( 'template-parts/content-grid' );
if ( $count % 2 == 0 ) {
echo '</div>';

In my customized template I've changed the standard loop to a "foreach" loop and link to the same file like this:

echo '<div class="row">';
foreach ( $child_categories as $child ){
$count++;
get_template_part( 'template-parts/content-grid' );
if ( $count % 2 == 0 ) {
echo '</div>';

Is there any reason why this shouldn't work?