Perhaps an economic policy could be effective for nations seeking to control their population. For example, instead of allowing income tax deductions for all children only the first two would be eligible. Following that, the parents PAY additional taxes. In addition, those choosing to have less than two children could receive tax credits. Government financed services could also be limited to two children. For example, the first two children receive free public education. Following that, the parents pay. Want more children without paying extra? Adopt!! No limit on the number of adopted children under such a system. In fact, adopted children could qualify for tax credits