Your son is a (Flying)Car Salesman, Your daughter a receptionist.

In the future, when all manufacturing tasks have become completely automated and robots and computers run the world, the only work that is available will be jobs in the service industry. Hence, boys sell the fancy cars, girls the makeup(just examples, no sexism on my end). While there may still be a market for haut couture, we are still left with the question of who will be able to afford to buy these things.

The only possible outlet for the economy will be retirees, assuming that all non-service jobs have been automated and the working class thus eliminated(or forced into extreme poverty/welfare).

These retirees will be your sons and daughters, once they have worked a few years and amassed plentiful and secure investments, likely in the company they work for. While there may still be management positions available, they will be few and far between because of the far better machine decision making and the availability of almost any luxury item at low low prices, i.e. you'd have to be a fool not to retire and simply live like a king on your modest dividends. Massive deflation will likely result from absolute automation, and, as long as young replacements keep arriving to fill the service jobs, most will likely work a few years out of high school and retire to a standard of living unimaginable today.

In order to prevent the extremely wealthy from disrupting the economy in foolhardy ways, seeking to become a zero higher than the rest(with little to no increase in physical comfort), the estate tax will have to be almost absolute. Simply to prevent large, destabilizing concentrations of wealth.

So relax, the economy of the future may well be more egalitarian than you imagine. It may require either ZPG or MPG(Massive Population Growth)