CREATE TABLE `tbl_p` (
  `p_id` bigint( 20 ) unsigned NOT NULL auto_increment,
  `name` char( 20 ) default NULL,
  PRIMARY KEY  (`p_id`),
  UNIQUE KEY `p_id` (`p_id`)
) TYPE=MyISAM;

CREATE TABLE `tbl_c` (
  `c_id` bigint( 20 ) unsigned NOT NULL auto_increment,
  `p_id` bigint( 20 ) unsigned default NULL,
  `name` char( 20 ) default NULL,
  PRIMARY KEY  (`c_id`),
  UNIQUE KEY `c_id` (`c_id`)
) TYPE=MyISAM;

INSERT INTO `tbl_p` (`p_id`,`name`) VALUES 
  ('1','Record 1'),
  ('2','Record 2'),
  ('3','Record 3'),
  ('4','Record 4');
COMMIT;

INSERT INTO `tbl_c` (`c_id`,`p_id`,`name`) VALUES 
  ('1','2','Record 1'),
  ('2','1','Record 2'),
  ('3','1','Record 3');
COMMIT;

SELECT a.p_id, IF(b.c_id is null,  0 , COUNT(a.p_id)) AS CHLD_COUNT
 FROM tbl_p a LEFT JOIN tbl_c b ON a.p_id=b.p_id
GROUP BY a.p_id;