Well, when you're doing the math on their subsidies, they homeschooled the kids, so if you figure the cost to the government for each kid K-College, they may be ahead of a traditional family.
$10,000/year for the 13 years is 130,000.
Pell Grants (5,730/year), Subsidized Loans (n/a since they don't do loans), and work study (involves actual work) don't add up to that much. Tax credits (2,500/2,000/year) helped out too.
They went to community college for 2 years and transferred to a state school. He said some got enough merit aid to go for free and some paid 5K/year. That fits with the less talented kids getting only a Pell Grant.
So ... 5,730 times 13 kids (eventually) times 4 years is 300K or so. (Tax credits are harder because they would only receive that for the kids that paid, and only for a fraction of the amount they paid, and we don't have enough info.) So the cost to the country for education is less than a 3 kid family. Or if you live in a high COL area, 2 kids.