If you have Windows XP Professional you can use the Local Security Policy to force kids off the computer and allow them to log onto the computer only at certain times. First, set Log on hours. Open a command prompt. Type in a net user command to set the users' hours. For example:

net user joey /time:M-F,18:00-20:00
net user bobby /time:M-F,6pm-8pm
net user sally /time:M,6pm-8pm;T,5pm-6pm;W-F,20:00-21:00

Notice that the user name is listed after the net user command. After the /time: switch you enter the day of the week and time frame they can log onto the computer.

Now you need to configure the Local Security Policy to log users off when they go past their logon hours. Go to the Run command and type gpedit.msc. Go to the following location:

Local Computer Policy\Computer Configuration\Windows Settings\Security Settings\Local Policies

Look in the right pane for Network Security: Force Logoff when logon hours expire. Double click on it and set it to enable. Restart the computer. Bingo! The kids will only be able to log on when you want them to, and the machine will force them to log off when it's time from them to get off the computer!