Hi I have been setting up Parental Control for a 9 year old kid on an Asus ZenPad S 8.0, which has Android 5.0 Lolipop installed.
I created a restricted account for him but tinkered trying to remove the guest option as he could bypass security by creating a temporary guest account.
In the end a part from install some aps like Time Limit, Screen Time, Internet Security, Family Time... I didn't actually do much as at some point after trying many different tools () I realised the tablet had to be rooted in order for the guest account to be disabled as described in this article http://slashgenie.com/how-to-disable-creation-of-android-guest-accounts-on-lollipop/ I decided not to root it as I am new to Android and I understood this voids the warranty and can create a "brick" :(
The strange thing is that now with the main owner/admin account I can create guest accounts but I can't create new accounts (I want to create another restricted account for his brother).
The "Add user or profile" option is disabled. This guy seems to have a similar problem Why can't I add any more user? But I only have two users the admin + the kid. Maybe with my tinkering of file explorer apps and sql editors I did actually manage to reduce the number of accounts to 1 (my original intention with fw.max_users=1)... but this should have show up on the file build.prop, which it doesn't, and how could I do that as my device is not rooted!?