I am not getting notified when the Find My iPhone app is used or even if I try searching via iCloud. How can I enable them?
You only get notified if you:
- Play a sound on the remote device
- Put the remote device on Lost mode
- Ask to be notified when it comes back online if the device is offline
Just watching the location of the device on the app or iCloud does not trigger a notification.
There may be ways of finding out, they are discussed in this question:
However, your son could enable Status Bar Icon so that the device shows the location services icon in the status bar when the location tracking is active.
Settings → Privacy → Location Services → Find my iPhone → Status Bar Icon This shows the normal location services icon (and not a special icon for Find my iPhone) if the device's location is being obtained through Find my iPhone.