Although reducing a country's birthrate might be a good economic strategy, but it has a very costly consequences. It could lead to labor shortage which results to nations depending on immigrants to fill diverse employment gaps. Most nations that promoted the reduction of childbirth has since dropped the policy and citizens are now encouraged to have more children. But it is now very difficult to encourage the citizens to have more children because the society have already been automated to have few children.
That is why it is important for the government to support families in this trying times because reduction in birthrate might be beneficial now, but the effect would not be good in future.
Having economic policy to reduce child giving or birth like birth control will not help for long time and you mentioning it already because of the effect that labour force, military and other jobs need to defending the country will reduce and that is dangerous Birth control policy is suppose to be temporary but what government can be doing to that is not for policy on that but to advise families on the economic situation and to give birth to what resources they have.