Pakistan does not need two child policy. What Pakistan needs is more investments on the major portions of the lands that are isolated begging to be used given the undiscovered resources like oils, fiber, gas, and other natural resources.
As soon as the economy starts to stabilize, the investment should be focus on building the technology like refinery that makes fully use of the undiscovered resources that is sitting in Pakistan.
Pakistan is huge land with lots of empty lands that are enough to cater at least 1 billion population.