Hello kathrine988,
We understand you are asking about viewing your son's texts and calls that come through his Apple Watch. We'd like to highlight some information in the article that you viewed before posting: Set up a family member’s Apple Watch - Apple Support
Using the Apple Watch app and Screen Time on your iPhone, you can manage the following:
* Communications limits and safety
* A schedule for time away from the screen
* Schooltime—a feature that limits certain Apple Watch features during school hours
* Mail and calendar settings for iCloud, Gmail, and other services
* Restriction settings for explicit content, purchases, and privacy
While you can manage settings for certain features on the Apple Watch, you may not be able to directly see those texts or phone calls on your device. You can also look at setting Screen Time restrictions for his device. That will help you set content restrictions and limits for those features and apps.
Use parental controls on your child's iPhone, iPad, and iPod touch - Apple Support
Take care.