Hey zlarice1,
It looks like you checked out the article about setting up Apple Watch for a family member. We understand you set the option for Screen Time to 'Contacts' only. This user guide will explain all the options for Communication Limits and what functions they provide:
Set up communication limits in Screen Time on Mac
5. Go to During Screen Time, then select an option below “Allow communication with.”
* Contacts only: Allow one-on-one and group conversations during screen time only with people in the family member’s contacts.
* Contacts and groups with at least one contact: Allow one-on-one conversations during screen time only with people in the family member’s contacts, and allow group conversations that include at least one person in the family member’s contacts.
* Everyone: Allow one-on-one and group conversations during screen time with anyone, including unknown numbers.
Is your son receiving a call from other family member's contacts?
Let us know and we'll see what the next best step would be.
Cheers!