>How will you decide who to give the basic income to?

>We'll choose the communities mostly for operational reasons. We're experts at delivering cash in very poor rural areas, and that's likely what we'll do with the pilot. Within the communities, we want to test a universal basic income, so we will enroll all full-time residents of a community.

- from the actual fund-raising page - https://givedirectly.org/basic-income

So, they aren't incentivizing baby making between families. But there may be between communities. That said, as people are elevated socioeconomically birthrate tends to decrease.

Edited to add: https://en.wikipedia.org/wiki/Income_and_fertility