You're right. Safe content header is a relatively weak solution. Strongest solution is either Microsoft or Apple stepping up to develop a child designed device from the ground up. It would have access to a limited walled garden of the Internet. The device itself is marketed specifically to children and has no advertising allowed on it. It also incorporates health guidelines and screen time limits, etc. that cannot be changed by the device owner or user, only by Apple/Microsoft. It is essentially a fascist phone. Admittedly, this would make an adult, unlocked smart phone a hot item on the youth black market, but hopefully most kids will be too lazy to save up the money needed to buy a black market unlocked phone before they're ready to watch porn and be inundated with endless advertising and doomscrolls.