Go to high risk areas. Offer a $2000 stipend for all 12+ females to get a 10-year birth control implant.
At 19, offer them another $2000 for a 10-year renewal.
Without all the new babies, people will go to school more, work more, innovate more, do whatever. In a generation, a small investment of a few million may result in a generational drop in crime, govt dependence, and more.
A kid born to a 12-year old will cost WAY more to society than 2 grand or even 4 grand. Let that mama wait until she's 29 to be fertile again - and it's completely voluntary. Sure, 2% won't do it. But 98% of people will go get that money.
Some millionaire did this years ago with Norplant... he didn't get many takers. It was immediately criticized as racist. He argued that it would stop the downward spiral towards poverty in many places but babies = checks, so people were easily fooled into buying the idea that he was trying to stop reproductive rights.
The system works exactly as intended.