Under age gambling is what both online and offline casinos don't joke with and some times why the government are so strict on gambling licensing os because of the KYC implementation which will help to expose any possible under-age registration and from the document verification you will be sure to be able to cash up with any of such possibility of underage.
Also, this is a hard battle for them because they won't determine if the verifications and IDs sent to them is the actual owner and that's why they are being stricter with such policies as for holding the ids and selfies. Because kids can just ask their parents to do it if they have the consent but as long as they have their own measures in doing it, there's no problem at all and they are only complying to the rules of the government that's being placed on them.
Children can verify simply by borrowing the identity of their parents or other adults. They may also have a photo of their parents' ID so they can verify it directly on the casino site. The casino won't know because the kids have already given up their identities. And the casino will agree to the verification.
This will enable children to gamble easily, especially if they know how to deposit and withdraw money. That may be one of the reasons why casinos implement KYC on their sites to avoid underage children registering. Even though it can't stop these children from registering, at least the casino has implemented or followed the rules set by the regulator.
The casinos are not to blame because they also do not require those children or even adults to register with their casinos. This is where parents play a role in being able to monitor their children when they use devices connected to the internet.
In the USA, this can be safely avoided with the SSN. Most of the casinos ask for an SSN and the OTP verification on the SSN-affiliated phone number follows that. Isn't this something that can secure children from registering on the casino? I think other countries are more vulnerable to such scams from happening. For example, in tier 3 countries the KYC's are easy to get and the illiteracy rate can make things worse for the parents and children. I mean even 16-year-olds can get their hands on their parent's phone, and easily get the KYC done with the OTPs. However, for the USA things could be very strict. It may not be that accessible for their children to get their hands on their parent's phone. I am not making any assumptions here, but it seems only proper guidance to our children can make things good for them. Maybe a strict environment where they understand the risk of getting involved with such things or websites.