Hi,
I bought one with Hub2 and 3 and I had to move to China, as it did not recognize the sensors, before I used everything in Sigapura in the current configuration, I no longer have access to an xiaomi smart plug because I bought it in their store in Portugal
In which region are you using the app? I tried Singapore, China, Portugal and when I choose to add children's devices it doesn't appear in the list of devices.