How much time do you think will take for teenagers to discover VPNs? Another impossible to enforce law made by people who don't know what they're doing.
It can also force pressure on the sites to more carefully filter minors to both avoid other jurisdictions following suite and criminal charges if continuing access to found to be granted French children.
> Another impossible to enforce law made by people who don't know what they're doing.
A law doesn't have to be 100% inescapable to be effective. In fact, this is an extremely enforceable law, and it is you who fail to see the application, either through ignorance or arrogance.
But it would be up to the parents to do this.
Most criminal laws are state laws, so you'll find at least[0] 50 different versions of any given crime. In some states, there is strict liability for an adult having sex with a minor (usually called something like sexual abuse of a minor; formerly often called statutory rape). In other states, the examples you gave would be valid defenses[1].
Laws requiring age verification have their own intent requirements. The Texas age verification law only applies when sites "knowingly and intentionally" distribute pornography[2] and imposes civil liability for sites that do so and fail to require either "digital identification" or use a commercial age verification service. There doesn't seem to be any specific requirement that they not make mistakes; it would probably default to negligence if it ended up in court.
[0] Some US territory is not inside any state, and there are federal laws that come into play when an act crosses state lines.
[1] Here's a statute from Alaska to that effect: https://www.akleg.gov/basis/statutes.asp#11.41.445
[2] https://capitol.texas.gov/tlodocs/88R/billtext/html/HB01181H...
IIRC the state of Texas was pushing for much worse, but basically the 'victim' was going to end up getting dragged through the mud and probably be forced to admit to all sorts of fraud and felonies involved in forgery, fraud secondary to forgery, and whatever other crimes are involved when you engage in crime with falsified government ID etc so they settled to avoid her having to testify.
If there is no need: Never