I don't think you've thought through the sentiment "But that’s the job of the parents, not the state" very well. Parents frequently want limited Internet access for their older preteen/early teen children, don't trust the private sector to implement this limited Internet access, and don't have the time to enforce this limited access themselves as they have to go to work and their children have to go to school anyway (and their parents want this limited access for them in school as well).
There are also easier options of no personal Internet access, and unrestricted access, but I suppose these are not very good for this stage of development.
As citizens we like to delegate aspects of our lives to the government; for example, I'm responsible for commuting to work on time, but we have delegated the maintenance of roads or public transport to the government, and this is something that could also be done by the private sector (private roads, private transportation), and ends up as a constant negotiation between citizen and government. Some polities like Germany and I think Sweden have subsidized education for children in exchange for mandatory public schooling by an institution either owned by the state or extremely highly regulated by the state.
There are also easier options of no personal Internet access, and unrestricted access, but I suppose these are not very good for this stage of development.
As citizens we like to delegate aspects of our lives to the government; for example, I'm responsible for commuting to work on time, but we have delegated the maintenance of roads or public transport to the government, and this is something that could also be done by the private sector (private roads, private transportation), and ends up as a constant negotiation between citizen and government. Some polities like Germany and I think Sweden have subsidized education for children in exchange for mandatory public schooling by an institution either owned by the state or extremely highly regulated by the state.