I think that this is awesome, but I have to say that none of these people should be having children. To bring a child into extreme poverty not only makes the poverty worse, but is an act of selfish cruelty perpetrated against a child that had no choice in the matter. I would make the basic income conditional: if you need this money, then don't have any more kids. I am not saying you must be rich to have children, but you should at least be able to feed and clothe them.
Asking people not to have children is not a good thing to do. Educate them on when/how but don't make a rule. It's a slippery slope to a dark place. Poverty doesn't affect a representative portion of the population. It's going to hit certain races, religions, groups etc harder. As soon as someone cries eugenics/racism, what do you say? You can't claim its being done to help group X if group X disagree. Don't start down the hole and it won't go wrong. That said - I can't imagine having a child in circumstances anywhere near these levels, and I too think this project is awesome.
The choice faced is either allowing unsustainable societies to die off, or subject ever more children to the unspeakable tragedy of being forced to live in those societies. This may sound harsh, but the world simply cannot sustain all of the children that humans choose to produce. The compassionate and humane thing to do is ensure that these people do not pass on their legacy of misery.
For many of the poorest families, having children is a way to generate more household income and a retirement guarantee of sorts. (Apologies for how callous that sounds.)
It seems to me that the birth rate has gone down nearly everywhere, as income has gone up. I believe that's likely to apply to BI as well.
In communities like the one described it's not uncommon for children to be an economic asset — yes, it's a cost for the first few years of their life, but once they are able to help tending animals and fields they can produce sufficient food to sell that they cover their living expenses.
What you are saying is akin to slavery, and it's wrong. Children shouldn't be conceived with an eye toward making them work on the family farm, and they certainly shouldn't be forced into manual labor.
