The apps installed are linked to the Roku account that the Roku device is linked to, so if you create a Roku account for them and only install a few apps, that's all they'll see other than the cruft ("On now", "Continue watching", "Recommended for you" or whatever it's called) that Roku keeps trying to foist on its users. There's only so much you can do, but I'd recommend adding a PIN to the Roku account so that purchases can't be made and channels can't be added without it. Also, don't use one of the Roku screensavers that advertise channels/apps (like City Stroll). Inevitably, they will unintentionally install one of the advertised apps and wonder what's going on.
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