[isleyaardvark]

Do these other countries described above know whether you had a kid or got divorced?

[deanmen]

Yes, in many European countries dependents and marital status changes are registered in a national civil registry, which the tax authority can query directly.

Countries like the U.S., Canada, the U.K. cannot easily do that without huge data-sharing reforms.

[fragmede]

Even the US knows that you've had a qualifying event, they're just being stubborn.

[vel0city]

The federal government doesn't always know if you've had a child or if you've died. Not even specifically the IRS, but its possible for you to have a child and never involve any organization that reports to the federal government.