Okay so I went down a bit of a rabbit hole on this one because I was curious what else is out there beyond the usual app recommendations, and here is what came up 
Workarounds for WhatsApp Monitoring That Do Not Get Talked About Enough
WhatsApp Web Session Monitoring
WhatsApp Web lets you link a device to a browser session. If you have brief access to your child’s phone, you can link their WhatsApp to a browser on your own computer. Any messages they send and receive will show up in real time on that browser tab. This is free, requires no app, and works until they manually log out the linked device. Check Settings > Linked Devices on their phone to see if they have found it.
Note: This only works while both devices are connected and the session stays active.
Google Activity Dashboard (Android)
On Android devices connected to a Google account you manage, Google’s My Activity section shows app launches, Google searches, and some usage data. Not message content but useful for building a picture of activity patterns.
Shared iCloud Account Monitoring
On iPhone, if WhatsApp backups are enabled to iCloud and you have access to the family iCloud account, the backup files contain message databases. Some tools like iMazing (a desktop app) can read those backup files and display WhatsApp conversations. This is a legitimate and legal approach for parents managing a family Apple account.
WhatsApp’s Own “Last Seen” and Read Receipts
Simple but often overlooked, if you are in a WhatsApp group with your child or have them in your contacts, “Last Seen” timestamps show when they were last active. Not who they talked to, but useful for checking late-night activity.
Setting Up a Secondary Device as a Mirror
Some parents set up a secondary Android phone with the same Google account as the child’s device. Certain app data syncs across devices. This is more technical and not always reliable but has been reported as working in specific configurations.
These are not perfect solutions but they are real options people actually use.