StingingVelvet: I mean it depends on what we're debating here. The policy is about online games only, so if we're debating micro-transactions and such then parents have full control over the child's access to significant amounts of money, if they want that. It doesn't even matter if they're around or not, or watching every moment of their child's playtime.
If we're debating "how much should kids play video games in general" and the parent wants to limit that time but finds it hard to effectively do so then that's another matter. Still there are ways they can do so, from passwords on the PC to after school supervision of some kind. Also if they ignore their school work and such to play too many games, it will reflect in their grades, and they can be punished. If you want to enforce some amount of physical exercise you don't need to be home that much to do so.
Some of these things can be challenging in our "both parents work" world today, I grant you, but those challenges are a LOOOOOOT better to deal with than the State regulating every aspect of your life and free time based on what old politicians think is proper.
I agree that state regulating free time is probably a bad idea (and fortunately, in real democracies, it won't fly as most people won't put up with that).
However, I often see the argument "its the parents job" given as a panacea solution for any pitfall a child might fall into and that's a dangerous fallacy.
I think we are expecting way too much out of parents here as we greatly overestimate the amount of control parents can exert on their children (the amount of time they can dedicate to their child, to what degree they can monitor their children at any time of the day or even at certain difficult ages, how much pull they'll have on their child compared to other outside influences).
For example, I don't think parents can effectively shield their children from the pervasive effect of ads targeting them (toys, junk food, etc), I don't think parents can fully control what their children eat (at home yes for the most part, but not when they are away from home) and in the era of smartphones and games you can play in a web browser, I don't think parents can really control how much online games their children play without help from the device manufacturers and in some cases, from the online game servers.
At some point, we need to go at the source and forbid/impose certain types of behaviours, for example by forbidding ads that target children, by forcing companies to list the calorie and other nutritional information on food sold, by listing the ingredients in processed food, etc.
Similarly, while implementing a social norm for all devices is indeed dystopian, you could potentially force device and/or game developers (the later would be required for things like online browser games as it would be hard to control this at the device level) to provide control mechanisms for parents to limit the amount of time their child plays.