That's not what I was saying. It is a pay-as-you-go system, meaning current taxes pay current benefits. So Joe's SS taxes that he paid in 1985 went to paying for beneficiaries in 1985. And workers today are paying for others' benefits today.

It's the ELIGIBILITY that I was referring to. To be eligible for benefits, you have to pay in for 40+ quarters (and for most people it's their whole working lives). It has nothing to do with whether your own children (vs other people's children) pay in or not as the OP suggested.

Now, does the funding run low when the ratio of payers:payees shrinks? ABSOLUTELY. That's already been happening for decades, as lifespans keep lengthening and we refuse to increase the retirement-benefit age enough to keep up. When SS first started, the average lifespan was actually SHORTER than the retirement-benefit age. 

Some say that the remedy is to crank out even more kids (that become payers). But that's shortsighted, as they later become beneficiaries.