And what do you do to the person who doesn't pay? Any legal action against them will cost more than $2000 per year per person who doesn't pay and thus be unprofitable. Jail time would also be a net loss on society.

$2000 per year is the interest income earned on $50,000 at 4% APR. If every individual paid just $25,000 per child born then by the time they are 18 the 25,000 would turn into 50,000 on the government's balance sheet. If you cannot pay then the government will lend you the $25,000 at 5% APR.

Require a total-life-time taxes paid of $50,000 and then constitutionally restrict the government to living off of the interest on its investments. Under such a system the government's stockpile of assets will grow as people die (and stop consuming) and new people are born (and add fresh capital).

The government currently owns over 120 trillion dollars in assets. If all they did was sell those assets and then lend the money received they could generate enough in interest income to eliminate all other taxes. If the government needs more money, just raise interest rates.