Of course they could. It would obviously be an enormous security problem. Apps would have to know the government ID of children. Nefarious entities could stage denial-of-service attacks against individuals.

Obviously China could do this. I am skeptical of the claim presented as hearsay without evidence.

If such a system exists, there should be easily found documentation for it.

"In addition, minors were required to use their real names and national identification numbers when they logged on to play and companies like Tencent and NetEase (9999.HK), set up systems to identify minors.

In July, Tencent rolled out a facial recognition function dubbed "midnight patrol" that parents can switch on to prevent children from using adult logins to get around the government curfew."

https://www.reuters.com/world/china/why-how-china-is-drastic...

That does not support the claim that apps are coordinating to restrict usage.

"in 2019, it passed laws limiting minors to less than 1.5 hours of online games on weekdays and three hours on weekends, with no game playing allowed between 10 p.m. to 8 a.m. It also limited how much minors could spend on virtual gaming items each month, with maximum amounts ranging from $28 to $57, depending on the age."

How could this be done without coordination?

In addition: "One of the first systems required by the government was launched in 2005 to regulate adolescents' Internet use, including limiting daily gaming time to 3 hours and requiring users' identification in online video games.[134] In 2007, an "Online Game Anti-Addiction System" was implemented for minors, restricting their use to 3 hours or less per day. " https://en.m.wikipedia.org/wiki/Video_games_in_China

Yes, coordination between apps would be the hard part and I see no evidence that it exists. There is a lot of writing in English that does not point to anything canonical from China. It does not make clear exactly what obligations are placed on app developers. I remain skeptical that coordination between applications is happening.

I would love to see any evidence of this. It should be easy if it exists as there would be documentation telling app developers how to use the central database. I would imagine an ecosystem of libraries would exist to make it easier for app developers to satisfy these obligations.