But then why is the number higher for 2adult1child (1 working) when compared to 2adult1child(both working). wouldn't child raising costs get added back in once both are working?

> In households with two working adults, all hourly values reflect what one working adult requires to earn to meet their families’ basic needs, assuming the other adult also earns the same.

From the page itself, first paragraph. Double the value under 2 adult (both working) to get the estimated household income.