determine if specific page is in list?

If you just need to remove, or ignore, it from $pages, use the exclude argument instead;

$pages = wp_list_pages( array(
    'exclude' => get_option( 'page_on_front' ),
    'child_of' => $parent,
    'parent' => $parent,
    'sort_column' => 'post_title',
    'title_li' => '',
    'hierarchical' => '0'
) );

I’ve used wp_list_pages as I assume this is the function you’ve intended to use (get_pages does not have a title_li argument).

If that isn’t what you were after, then just loop over the pages to determine if it’s there;

foreach ( $pages as $page ) {
    if ( $front_is_here = ( $page->ID == $front_id ) )
        break;
}

if ( $front_is_here ) {
    // front page is among pages
} else {
    // front page is *not* among pages
}