Dependent isn't just children, and if you are separated or unmarried it may not even be your children that count as dependents. It doesn't even require you to be the legal guardian.

https://www.irs.gov/help/ita/whom-may-i-claim-as-a-dependent

But almost no one claims those kind of dependents. And furthermore, the government could just say, "last year you claimed these people as dependents, and we checked and they're all still alive, so we'll assume they still are".

Or even just have it be a field on your W-4 to keep up to date.