Back when the US federal courts didn't suck, they put a temporary injunction on an online age verification law from the 90s (COPA), adding

the Court is acutely cognizant of its charge under the law of this country not to protect the majoritarian will at the expense of stifling the rights embodied in the Constitution. […] I without hesitation acknowledge the duty imposed on the Court and the greater good such duty serves. Indeed, perhaps we do the minors of this country harm if First Amendment protections, which they will with age inherit fully, are chipped away in the name of their protection.

Age verification laws threaten online safety, privacy, & fundamental liberties, they don't restrict sources outside their jurisdiction, they rely on criminal sanctions & law enforcement resources, and they're unnecessary & ineffective. In the balance between fundamental rights & other "compelling interests", government has a duty to minimize compromises of fundamental rights in meeting its "compelling interests", and age verification laws fail to strike that balance.

Laws can do better than impose restrictions & penalties. When that same court made the injunction permanent, the judge wrote

Moreover, defendant contends that: (1) filters currently exist and, thus, cannot be considered a less restrictive alternative to COPA; and that (2) the private use of filters cannot be deemed a less restrictive alternative to COPA because it is not an alternative which the government can implement. These contentions have been squarely rejected by the Supreme Court in ruling upon the efficacy of the 1999 preliminary injunction by this court. The Supreme Court wrote:

Congress undoubtedly may act to encourage the use of filters. We have held that Congress can give strong incentives to schools and libraries to use them. It could also take steps to promote their development by industry, and their use by parents. It is incorrect, for that reason, to say that filters are part of the current regulatory status quo. The need for parental cooperation does not automatically disqualify a proposed less restrictive alternative. In enacting COPA, Congress said its goal was to prevent the “widespread availability of the Internet” from providing “opportunities for minors to access materials through the World Wide Web in a manner that can frustrate parental supervision or control.” COPA presumes that parents lack the ability, not the will, to monitor what their children see. By enacting programs to promote use of filtering software, Congress could give parents that ability without subjecting protected speech to severe penalties.

I also agree and conclude that in conjunction with the private use of filters, the government may promote and support their use by, for example, providing further education and training programs to parents and caregivers, giving incentives or mandates to ISP’s to provide filters to their subscribers, directing the developers of computer operating systems to provide filters and parental controls as a part of their products (Microsoft’s new operating system, Vista, now provides such features, see Finding of Fact 91), subsidizing the purchase of filters for those who cannot afford them, and by performing further studies and recommendations regarding filters.

Adult supervision, child education on online safety & literacy, parental controls & filters are more effective at less expense to fundamental rights. With client-based filters alone, numerous legislative studies (eg, COPA Commission, NRC report) & court decision findings pointed out more effectiveness than age verification laws in that filters

• block at the receiving end, so they aren't limited by geographic origin (outside legal jurisdiction)
• operate on any protocol (not only HTTP or successors) regardless of dynamism (eg, live chats or media)
• give parents control to tailor filters per child (eg, age-appropriateness)
• can more granularly filter out sections of a web page rather than entire web pages or web sites
• can filter out other kinds of objectionable content (eg, violence, hate speech)
• can be monitored with logs & corrected.

They also don't obstruct adults who don't use them. Newer studies continue to confirm that.

Lawmakers are aware the studies they've commissioned recommend more effective & less invasive alternatives, and they could pass laws following those recommendations, yet they don't. Government is simply failing in its duties to make better laws that respect civil liberties & defend those civil liberties from unjust laws.