I took the cost of living from Economic Policy Institute's Family Budget Calculator, and their documentation [1] is particularly interesting to sift through.

In particular, the child care costs are apparently broken down like this: One parent, one child = cost of 4-year-old care One parent, two children = cost of 4-year-old care + cost of one school-age child One parent, three children = cost of 4-year-old care + cost of two school-age children Two parents, one child = cost of 4-year-old care Two parents, two children = cost of 4-year-old care + cost of one school-age child Two parents, three children = cost of 4-year-old care + cost of two school-age children

And they assume the school-age children to require both before-school and after-school care.

As for comparing a cost of living for a two-parent household with the income of a single worker, I could only make that assumption because...how would I be able to extrapolate the household income of a two-parent family from BART salaries? As imperfect a solution as it is, I still hope that it will give insight, since my hope was not to shove any particular opinions on anyone, but rather just a tool for exploration.

[1] http://www.epi.org/publication/wp297-2013-family-budget-calc...