Birth rate
As of 2017, Niger has the highest birth rate in the world with 49.443 per thousand people. 
Japan has one of the lowest birth rates in the world with 8 per thousand people.
While in Japan there are 126 million people and in Niger 21 million, both countries had around 1 million babies born in 2016.
Girl
Child marriages, where girls are married at young ages (often forced and often to much older husbands) remain common in many parts of the world. They are fairly widespread in parts of the world, especially in Africa, South Asia, Southeast and East Asia, the Middle East, Latin America, and Oceania. The ten countries with the highest rates of child marriage are: Niger, Chad, Central African Republic, Bangladesh, Guinea, Mozambique, Mali, Burkina Faso, South Sudan, and Malawi.