that's not either

See the first row in this table: https://livingwage.mit.edu/counties/06075

Compare 2 adults (1 working) 3 kids to 2 adults (both working) 3 kids

First off, you'd expect it to be

     1 adult = X
     2 adults = X + X(0.?) 

Where 0.? is something less than 1 because 2 adults need less than 2x the money

Similarly for kids

     1 kids = Y
     2 kids = Y + Y(0.?)
     3 kids = Y + Y(0.?) + Y(0.?)

You'd expect 2 kids to be less than 2x 1 kid. And you'd expect 3 kids to be les than 1x + 2x 2nd kid. Each kid is cheaper for various reasons like hand-me-downs etc...

But instead, under 2 adults 1 working we see

     1 adult  = $29.31 (from one adult)
     2 adults = $41.83 (so X + X * 0.42)

     2 adults 1 kid  = 50.47
     2 adults 2 kids = 54.77 (so + $4.30)
     2 adults 3 kids = 63.97 (so + $9.19)

Why does the 3rd kid cost more than the 2nd?

Then you can also compare 1 adult 3 kids with 2 adults both working + 3 kids

     1 adult + 3 kids                 = $107.95
     2 adults (both working + 3 kids) = $55.67

Assuming that $55.67 is wages for each that means we're comparing

     1 adult + 3 kids                 = $107.95
     2 adults (both working + 3 kids) = $55.67x2 ($111.34)

We already established that above that adding one adult is only $12.52 a month yet here, suddenly that adult only costs $3.40 a month.

Again, these are nonsense numbers.