I’m looking for a way to get my child’s messages that he’s recently deleted messages

If your child is at all capable of basic tradecraft, those deleted messages are gone, and the only remaining source would be from another party in the conversation, if the messages were preserved there.

In general: Recover deleted text messages on your iPhone or iPad - Apple Support

SmithN254 Said:

"I’m looking for a way to get my child’s messages that he’s recently deleted messages"

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Troubleshooting Deleted Messages:

What to Consider:

A. Restore from Today's Backup:

Restore your iPhone from a backup of it that contains these messages, and you could recover them.

B. Check Messages App:

If messages was enabled on your iPhone along with your Apple computer, then check and see if the Messages app is enabled on your Mac to see if it exists in it. You'd start up your Mac, not connecting to the Internet, and open the Massages app. Then proceed from there with retrieving it. Important: Be certain you do not connect to the Internet while booting up, as syncing would delete it. So, power off your router to avoid the connection.

Elsewise, if they're gone, they're gone. That's just the way it is :(

You'll likely be unable to do so.

If they sync using iCloud messages, a deleted messages deletes everywhere immediately.

If they do not use messages in iCloud, but regularly back up to iCloud or a computer, the device would need to be factory reset and restored using the backup.