Let's assume you're right that they don't have a simple table that shows parentage of every SSN, sounds plausible that they wouldn't at least to start, but on the other hand, (for people who don't add or remove spouses or kids from their household) it's arguably VERY common for kids to persist with the same parent(s) from one year to the next.
I don't think anyone is saying "All taxes should be automatically calculated to the final numbers" -- just that for instance, when I filed last year with a spouse and 2 kids, a default calculation could be done this year that assumes an unchanged household.
And anyway, just as TurboTax does, the IRS could maintain a simple fact database for you for you to sign in and indicate what SSNs are part of your household, with the bonus that it would detect a duplicate claim for the same kid up front and show you that someone else (e.g. your ex) is claiming them and that you should get them to remove them to avoid both your returns being incorrect. The complexity for a taxpayer of signing in to IRS to manage household members, address, etc. with IRS is an order of magnitude less than that of tax prep they have to do today.
I don't think anyone is saying "All taxes should be automatically calculated to the final numbers" -- just that for instance, when I filed last year with a spouse and 2 kids, a default calculation could be done this year that assumes an unchanged household.
And anyway, just as TurboTax does, the IRS could maintain a simple fact database for you for you to sign in and indicate what SSNs are part of your household, with the bonus that it would detect a duplicate claim for the same kid up front and show you that someone else (e.g. your ex) is claiming them and that you should get them to remove them to avoid both your returns being incorrect. The complexity for a taxpayer of signing in to IRS to manage household members, address, etc. with IRS is an order of magnitude less than that of tax prep they have to do today.