The IRS already has W-2s and 1099s, which cover ordinary pay and retirement investments, and enough money has probably been automatically withheld already. Remember that this isn't automatic billing, but automatic filling. They'll send you the form, and you can insert the number of children. If your taxes are much more complicated than that, you can probably afford TurboTax.
In the meantime, the same lobbyists who created this scheme are trying to prohibit IRS from developing its own free filing system: