Parent Control option now Google Chrome Supervised Account Beta ended?

I have been using Supervised Accounts in Chrome for my young children. Google is closing this service and not replacing it with anything for Desktop/Laptop computers - even Chromebooks.

I have looked at browser pluggins/extensions, but all of these can be simply disabled or uninstalled so are not going to be any use.

My ISP has parental control, but I've always used a strict Whitelist approach which I can't reproduce using my IP's service.

I have tried openDNS, but services such as these again don't support Whitelists. They also create problems on sites which are Whitelisted, preventing them working properly. I see parts of the whitelisted page fail to load because parts are loaded from other domains not on the Whitelist.

I have even experimented with setting up my own proxy server, but again parts of the allowed whitelisted pages fail to load because they are loaded from another domain.

What I've learned is the best solutions are client (browser) based, but because browser security now prevents the design of extensions which cannot be disabled and uninstalled this whole class is useless for this purpose.

Have I missed an option which does work well?

(My kids never use the net unsupervised and have their own desktop accounts.)