Can I add a channel on a Roku device and only have it appear on only 1 device ?
If the Roku devices are linked to same account the answer is no. You can create separate accounts using a different email address for the second account and then link one of the devices to that account. Roku accounts are free. If the channel is one you don't want children to see you can logout of the channel on one device and not share the login credentials. This method will not work if the channel automatically logs in on all devices and some do.