I was just playing with kid-control and found that it would only create the filter rules when the device tried to communicate.
Also, you can't have an end time of 00:00:00 for any of your time settings. Setting 00:00:00 for any setting means the rules will never start.

I've setup kid control and it works for IPv4, but the computers can still communicate via IPv6

How can I also restrict IPv6?