Disable or lock parent pages from being edited in wordpress admin

Yes there is. Save this code as plugin and activate one. Plugin will lock all pages that has children from edit.

<?php
/*
Plugin Name: Lock parent pages form edit
Plugin URI: 
Description: 
Version: 0.1
Author: Alexey Selin <[email protected]>
Author URI: http://wordpress.stackexchange.com/users/7314/alexey
*/

function lock_parent_pages_from_edit( $capauser, $capask, $param){
    global $wpdb;
    $post = get_post( $param[2] );
    $children = get_pages('child_of=".$post->ID);
    if( count( $children ) > 0 ) {
        if( $param[0] == "edit_page" ) {
              foreach( (array) $capask as $capasuppr) {
                 if ( array_key_exists($capasuppr, $capauser) ) {
                    $capauser[$capasuppr] = 0;
                 }
              }
        }
    }
    return $capauser;
}
add_filter("user_has_cap', 'lock_parent_pages_from_edit', 100, 3 );
?>