You may want to try OpenDNS Family Filters: https://support.opendns.com/hc/en-us/articles/228007127-FamilyShield-Computer-Configuration-Instruct...
In Hitron modem: basic>dns. Change the dns address to the Open Dns family filter.
It is working on the Cisco router as well https://www.opendns.com/setupguide/
