Comment by lelandbatey

No, it's because their model puts dollar values on the labor contributed by non-working adults w/r/t raising children. So in that case, it could be that 1adult1child is slightly higher because of the need to pay for childcare, while the food/insurance/clothing etc of the additional adult in 2adult1child is offset by the fact that the non-working adult will conduct childcare and thus that expense goes away.