Welfare is not the only solution to this problem. If minimum wage is not enough to allow a single mother to pay for child care, then we should just offer free child care, financed by taxes. Mom still has an incentive to work for a living, but is much better off. Scandinavian countries demonstrate that this works very well.
>Why should anyone in the US be guaranteed comfort when there are children begging in the street in Mexico or India?
Because as I said, the US as a society is incredibly wealthy. It's possible with a few political tweaks to fix this, and not a single person will be noticeably worse off. There's no real reason not to fix it, except for the extraordinary greed of a few.