Educated well at the elementary level is what I'd go for. But some of that Billion would go to ensuring, as far as possible, a certain amount of education and counselling for the parents and older siblings of these kids. That way what they learned at elementary school would not be sabotaged by those these kids regard as their role models. For much of this Billion would go not just on 'reading, writing and ';rithmetic, but on such things as values, qualities...and what makes for a more sound society.
Why simply waste it on academic subjects!