Note the difference between "lots of writes" and "lots of concurrent writes". "Lots of writes" in succession without heavy concurrency support is just fine for desktop/mobile apps. It is not okay for busy webapps.
I use SafeDNS which filters adult content (plus many more categories), without forcing YouTube Restricted Mode. But, you can opt into YouTube Restricted Mode if you choose.
With age comes responsibility, so with time and coaching we remove restrictions. But it takes time, and I'm not willing to sacrifice my child's education in the meantime for YouTube and gaming distractions. I've grown to recognize there are certain distractions that are simply too difficult for young children to refuse.
Practical tip for parents here struggling with the problem of 'distractions during school hours': use a DNS filtering service.
I use the Family package from SafeDNS and I'm generally happy. It is also cheap at $20/year. I like SafeDNS because they provide a Desktop client that prevents tampering.
You can configure different profiles such as 'Education', 'Creative' and 'Default' for different modes you want to put your child's computer on - remotely. So during schooling hours I configure their computers to be on 'Education' mode, but if they want to just do Scratch or some other brain-stimulating activity, I put it on 'Creative' mode. For free time I'll put it on Default which I've configure to allow YouTube.
I configure each profile to block preconfigured vendor-supplied site archetypes such as Videos, Gaming, Advertising, Shopping, Chat etc. I have full control over each profile type. I can also whitelist a domain if they get in a snag.
I'm sure there are other good DNS filtering service providers, but this one is the one that worked best for me.