Insert into a table with forign key within the trigger of the other table in MySQL - mysql

Question

I have a parent table in MySQL as follows:
CREATE TABLE `parentTBL` (
`id` int(11) NOT NULL AUTO_INCREMENT,
`source_name` varchar(255) DEFAULT NULL,
`loc1` smallint(5) unsigned DEFAULT NULL,
`loc2` smallint(5) unsigned DEFAULT NULL,
`extra_info` json DEFAULT NULL,
PRIMARY KEY (`id`)
) ENGINE=InnoDB AUTO_INCREMENT=15 DEFAULT CHARSET=latin1;
a child table:
CREATE TABLE `childTBL` (
`id` int(10) unsigned NOT NULL AUTO_INCREMENT,
`source_names_id` int(10) unsigned NOT NULL,
`locations_id` int(10) unsigned NOT NULL,
`extra_info` json DEFAULT NULL,
PRIMARY KEY (`id`),
KEY `fk_childTBL1_idx` (`source_names_id`),
KEY `fk_childTBL2_idx` (`locations_id`),
CONSTRAINT `fk_childTBL1` FOREIGN KEY (`source_names_id`) REFERENCES `source_names` (`id`) ON DELETE CASCADE ON UPDATE CASCADE,
CONSTRAINT `fk_childTBL2` FOREIGN KEY (`locations_id`) REFERENCES `locations` (`id`) ON DELETE CASCADE ON UPDATE CASCADE,
) ENGINE=InnoDB DEFAULT CHARSET=latin1;
and these 2 tables:
CREATE TABLE `source_names` (
`id` int(10) unsigned NOT NULL AUTO_INCREMENT,
`source_name` varchar(255) DEFAULT NULL,
PRIMARY KEY (`id`),
UNIQUE KEY `source_name_UNIQUE` (`source_name`)
) ENGINE=InnoDB AUTO_INCREMENT=85 DEFAULT CHARSET=latin1;
CREATE TABLE `locations` (
`id` int(10) unsigned NOT NULL AUTO_INCREMENT,
`loc1` smallint(5) unsigned DEFAULT NULL,
`loc2` smallint(5) unsigned DEFAULT NULL,
PRIMARY KEY (`id`),
UNIQUE KEY `loc1` (`loc1`,`loc2`)
) ENGINE=InnoDB AUTO_INCREMENT=43 DEFAULT CHARSET=latin1;
I have a trigger for parentTBL table before insert like this:
CREATE DEFINER=`root`#`localhost` TRIGGER `myDB`.`parentTBL_BEFORE_INSERT` BEFORE INSERT ON `parentTBL` FOR EACH ROW
BEGIN
INSERT IGNORE INTO source_names (source_name) VALUES (NEW.source_name);
INSERT IGNORE INTO locations (loc1,loc2) VALUES (NEW.loc1,NEW.loc2);
INSERT IGNORE INTO childTBL (source_names_id,locations_id,extra_info) VALUES (????,????,NEW.extra_info);
END
and I want to insert into childTBL and 2 other tables before inserting into parentTBL but I don't know what should I put in ???? fields in above trigger (third INSERT IGNORE. Move scroll to right)?
(It should be noted that I don't want to use SELECT because I have some millions records and fast insertion is important to me and also my problem is not solved with LAST_INSERT_ID() because it is possible that I need the source_names_id which is added before last_inserted in source_names table.)