A good slap to the back of my head used to keep me from changing the settings on my parent's televisions without permission.
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Unfortunately, there are two ways to Factory Reset a Roku device/RokuTV.
1. Settings/System/Advanced System Settings/Factory Reset
2. Physical reset button on the Roku device/RokuTV (press and hold 30+ seconds).
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If you wish to allow the "kid" access to their own Roku account (email address), you can purchase another Roku device and just plug it into another HDMI port on the TV. Then they can just switch to that HDMI port and use "their" Roku device without having to factory reset your Roku device/RokuTV.
Roku Community Streaming Expert
Just another Roku user... I am not a Roku employee.
Insignia RokuTV, Ultra 4660, Premiere+ 3921, Express 4k+ 3941, Streambar 9102