@NetPingS,

So from what I can tell, the Tether Parental Controls monitors the incoming connections to the devices, and will block any that are attempted when the setting is on. Unfortunately, this does mean that any communications that do not require the connection to be refreshed, such as a Discord Call, will not be automatically blocked at the time, as it is not shutting down the network connection to the device, just blocking communications from outside of the network from reaching the device.

If I am correct, there is an option to disable the internet access on the application for a specific device. Does this block the existing connections?

Another option may be to configure the guest network, so that you can disable the literal network to his devices. However, you would have to prevent them from accessing the normal network password. Otherwise, it may be required to set up parental controls on the devices themselves.