In all but the most niche cases, they do in fact know that you had a kid. That being said, most things they have a pretty good idea about (or could) and they could easily adopt the system that they do in a lot of other countries where the government sends to a tax form all filled out that says, “we think you owe this much.” Then you just provide the exemptions you listed.
This would save a considerable amount of time when I file my taxes by just being able to double check they got cost basis correct on stocks sold and applied appropriate credits for mortgage interest and what not.