Biometric identification technology is indeed very effective, the system detects it in just seconds, I haven't heard of anyone who can fool the system. Too many gambling sites and minors will definitely find other solutions so they can gamble, the most to be considered is their connection and the role of parents who should monitor whither they access website, restrictions that must be increased.
By far it is best but all have weaknesses. The best protection is education from an early age. How does a child know what is ok and what is not. I think if parents notice this all will go well. Relying on the system of service providers and the government will not be effective enough to displace underage users. They have to work together so as to create mutually beneficial circumstances.