I want to track my sons phone, what is the best way without him knowing?

There are no means of tracking it without him knowing. Find My and other tracking apps in the App Store require you to request he allow you to track. He can refuse even after initially accepting it.

Whether anyone’s personal device is tracked by another is something the owner of each device has control of. Location sharing is not enforceable on another person’s private device.

You would have to remove his AppleID from the device and install a remote managed profile to force the device to be traceable without his consent (something companies can do with company devices under a remote managed deployment where personal accounts are not allowed on the device).

Hmmm what i suggest is this https://support.apple.com/guide/iphone/locate-a-family-members-missing-device-iph6231f621a/ios but to locate it without him really noticing from the seetings might be hard

Find My.