As a Hub by Securly user, the SecurlyHome app notifies you of any new device on your network to help you filter it if required. The new device is detected based on its MAC ID. A new MAC ID is interpreted as a new device.
Most laptops have the option of connecting to the internet via a cable or WiFi. Both methods generate different MAC IDs for the same device which leads the system to interpret it as two different devices. So if your child’s laptop was connected to the WiFi when you included it in the Filtered Devices list, and later if it is connected via a cable you will receive a new device notification. In such a situation you would need to add that MAC ID in your Filtered Devices list so that the device is filtered irrespective of whether it is connected to WiFi or cable. (Learn how.)
You could also rename the device so that it is identifiable no matter what method is used to connect to the internet. (Learn how.)