Sagemcom F5359 parental control filter urls. How to?

Hello, I have Sagemcom F5359 modem or kpn box 12, and I need to setup parental control to limit access to some specific sites by filtering urls, but looking at the modem settings it is only possible to completely disable internet on specific devices. Unfortunately that option is useless for me because kids still need access to internet, for example to do homework, etc. I also could do this quite easily with 6 years old modem from Vodafone.
So how it is possible to do with KPN?