What exactly are they trying to limit? Is it restricting access to a certain time of the day or a certain amount of time they can stay logged in?
A bit of both I believe.
There are definitely a set of hours that they don't want the kids logged in, but I also think that they want a fairly high level of flexibility. I.e. ensure there is no late night use on school nights, unless there is no school the next day on what would normally be a school day.
so you could just give the kids a diff user account than the parents to use, and hence a diff password...
its not so simple to limit their abilities to certain applications or functions within applications.
Yes, but that is too simple, the kids can login at will. And I don't think you can limit logon hours unless the pc is part of a domain, and that would be too rigid.
The first thing they did, was to enable the guest account so they could log in at will.