I have kids. I'm happy they _always_ ask for a password... Free apps can be malicious e.g giving away location to parties unknown. But still you're right - this could be an option users can decide.
If I had a child I'd want to be able to let them use my phone but only in a special mode that allowed access to a limited number of whitelisted websites & apps.
http://www.schneier.com/blog/archives/2012/07/all-or-nothing... http://cups.cs.cmu.edu/soups/2012/proceedings/a2_Hayashi.pdf
But: yes.
I'd like my phone to offer a few different "shells" of access:
- Emergency calls.
- "Share" or "play" mode. Selected photos or apps.
- "Mobile" -- ready access to stuff I need, but not distractions (the "Car Panel" on some Android phones is somewhat like this, but I'd appreciate if it didn't encourage use while driving).
- "Full" complete and potentially immersive access.