How much do you need to "retire" to real estate?

[Joe A.]

Curious as to what everyone thinks, just a question for fun...

-What amount would you say that a 30yr married person needs in CASH in order to support a spouse and two children in an average middle class town.  Cash can be used to invest in RE rentals (not fix and flips).  Assume rentals will earn around 8-12% cash-on-cash per year.  Person must buy properties in cash for simplicity of argument.  Income from rentals and savings must cover healthcare costs for spouse and two children (assume infants), a primary residence, 2 modest cars, a modest middle income lifestyle (1 vacation per year, 3k budget). eventual retirement (though assume rental income will continue until death).