Kevin would like to have a time limit for his kids on the iPad. Leo says that there's no way to set a time limit on the actual iPad, but he can enable parental controls to limit his kid's activity. He could also set up a time limit restriction through his router. It also has access controls. He can find the MAC addresses and block them. He should look in the router under 'access control lists' and he can block machines by times, in addition to blocking content. Another good way to do this is by using OpenDNS.com.
The chatroom also says that Time Lock is an app for the iPhone and iPad that will enable the user to lock down an iOS mobile device by time. It costs just $0.99 and it's ideal for what Kevin needs.