Why did China implement a one-child policy? What are the benefits of having only one child? How does infanticide (killing of infants) relate to this issue?

China implemented the one child policy to bring down the population, as they where reaching one billion people. Essentially the benefit of having one child, is the economic price that lowers of only taking care of one child; the less people you need to take care of, the more money you have. China would usually have infanticide epidemic concerning females, as they viewed males as more essential to the household.