There are many devices for this but a consumer friendly version would be FingBox. It’s based on the Domotz platform. You will be notified if someone tried to join. You can autoblock all connection. You can assign users and devices to those users. In the case of our kids you can set access times to the network. It will also speed test your network at intervals and send you a report. One nice feature is it will do local speedtest against your access point so you can see how weep the reception is in a given room in comparison to where your access point is located. I recommend it!