This should be the time for open-source developers to use their common sense to decide whether we should push back. If California wants to create its own Protect the children operating system, it should bear the cost and responsibility for this alone, and not export any of the sketchy political agenda to the wider open source community.
It's the law. If you live in the United States, and a minor in California uses your OS that didn't check age, you could be liable for up to $2500 per occurrence. That can add up quickly if California schoolkids discover your OS does an end run around the law. When ruin is the alternative, compliance becomes non-negotiable.
"There is no justice in following unjust laws." - Aaron Swartz (Guerilla Open Access Manifesto)