Add pagination to WP_Query

Fixed by adding the below code.

<?php 
                        $paged = ( get_query_var( 'paged' ) ) ? get_query_var( 'paged' ) : 1;
                            $child_query = new WP_Query(array('post_type' => 'blogpost', 'orderby' => 'date', 'order' => 'DESC','paged' => $paged));
                            while ( $child_query->have_posts() ) : $child_query->the_post(); ?>
                                <div class="single-post">
                                    <div class="leftContent">
                                        <?php 
                                            $image = get_the_post_thumbnail($post->ID,array(300,180)); 
                                            if($image == ''){
                                                $image = wp_get_attachment_image(11270,array(300,180));
                                            }
                                        ?>
                                        <a class="title" href="<?php the_permalink()?>"><?php echo $image; ?></a>
                                        
                                    </div>
                                    <div class="rightContent">
                                        <a class="title" href="<?php the_permalink()?>"><?php the_title()?></a><br>
                                        <div class="post-date"><?php the_time('F jS, Y') ?> by <?php echo get_the_author() ?></div>

                                        <div class="content">
                                            <?php echo excerpt($post->ID,320); ?>
                                            
                                        </div>
                                        <a href="<?php the_permalink()?>" class="readMore" >Read More</a>
                                    </div>
                                </div>
                                
                        <?php 
                            endwhile;
                        ?>
                        <div class="pagination">
                        <?php 
                            echo paginate_links( array(
                                'base'         => str_replace( 999999999, '%#%', esc_url( get_pagenum_link( 999999999 ) ) ),
                                'total'        => $child_query->max_num_pages,
                                'current'      => max( 1, get_query_var( 'paged' ) ),
                                'format'       => '?paged=%#%',
                                'show_all'     => false,
                                'type'         => 'plain',
                                'end_size'     => 2,
                                'mid_size'     => 1,
                                'prev_next'    => true,
                                'prev_text'    => sprintf( '<i></i> %1$s', __( 'Newer Posts', 'text-domain' ) ),
                                'next_text'    => sprintf( '%1$s <i></i>', __( 'Older Posts', 'text-domain' ) ),
                                'add_args'     => false,
                                'add_fragment' => '',
                            ) );
                        ?>
                    </div>
                    <?php wp_reset_postdata(); ?>
                    </div>