The Nippy Web Browser is designed form the ground up with the child behaviour in mind.
Session Times can seperate sibling sessions and also prevent ad hoc computer usage.
If you need to access your computer at specific times, you can, without tears, using session times.

• Some Nippers are opportunists.
  You can define when they have an opportunity to logon to the browser.
  This feature is for your convenience as well as their's.
• Graphical Scheduling
  You can click and drag blocks of time in the Session Times widget.
  Precise adjustment to times is available with the arrow keys or the mouse wheel.
• Sessions Times provide Nippers with Certainty.
  If they know when they can have a session, Nippers may order their behaviour accordingly.
  A routine is liberating for Nippers. They don't have to nag to get what they want.

• Each child has their own Session Times setup.
  You can have as many sessions during each day as you like.
  If your child has a Wednesday afternoon play session at 1:30 you can make sure their session ends in time to get ready and go.

• Check the Use Session Times checkbox to only allow access during defined sessions. Leave unchecked to allow the user to log on at any time.
  See "Session Times" image below.

Portion of the Limits Tab screen in the Browser Content Control Panel