Another solution is two go into the app on the Roku device that you have in the child's room and logout of that app. (Do not remove the app, that will remove it from all devices). If the app has a password required, the app will appear but will not be able to accessed from that Roku device.
Sadly, even settings on one channel on your Roku spreads to every channel on every Roku device you have. I am replacing ALL Roku devices and just buying smart TVs without this **bleep** device attached to it. Roku makes it impossible to customize each device/channel, so good by Roku.
This is so annoying, I don't want to have to get another, I use the app on my phone to control the devices (my kids' bedroom tv's) we don't have cable hookups in their rooms so this used to be convenient. It's kind of a mess now because my tween wants youtube on her tv but we don't allow that for the 8 year old. you should be able to have different profiles for different devices if you want to.