The person who made up this question claims that we should use "however" instead of "though" here. I strongly disagree with him. What do you think?
As a matter of fact, both of them would work here.
It doesn't matter whether you use 'though' or 'however'. The main problems are logical.
1. "The urban ones earn money, though" only makes sense if the rural children don't earn any.
2. The rural children earn less money than whom? If the answer is "the urban ones", then it's obvious that the "urban ones earn money, though".
This should be one consistent sentence.
"Rural children hired to work on farms get less money than urban children." This could still be ambiguous if the urban children are not working on farms.
The sentence sounds odd to me because of this ambiguity- wouldn't the urban children be making more money in the towns than on farms? I'd be more likely to pay rural people more for working on farms as they're more likely to know more about it.
Rural children hired to work on farms get less money than they deserve.
...than they used to. ...than they get working elsewhere.
...than they do blisters.
...than urban children doing the same work.