I foresee almost all online services requiring an age verification (the kind everyone hates when porn services use it) and then an age tiered product being offered. I could easily see a 2 or 3 tier youtube, for example.
Tier 1 would be full adult access no different than today.
Tier 2 would be very limited youth access, utilizing big data to identify when kids are trying to cheat by using multiple accounts. This would have both content and time limits, but the content filters would be fixed based on the most restrictive criteria.
Tier 3 would be "premium" youth, unlocked with a subscription of course. It would by default permit both the restricted youth content, but also educational content that might have otherwise been automatically blocked by the generic tier 2 standard (things like biology class videos, current event discussions, etc). It could also have parental controls that permit modification of usage time limits and various filter settings to allow or block content such as "biology", "politics", "violence", "religion", etc.
They could monetize the crap out of this, especially since many school districts have standardized on google classroom and you can't block youtube without also blocking google classroom, which can't possibly be an accident. Schools using google classroom would have to pay an additional premium to first authorize registered students into the age restricted service tier, and then they'd have to pay AGAIN to unlock educational content that would be somehow mysteriously blocked under the free tier 2 service.