Green stamps for the right to have children

Economist Kenneth Boulding suggested that at birth, every female in the country be endowed with a certain number of green stamps giving her the right to a certain number of children when she reaches child-bearing age. Depending on the population, the value of these stamps may vary from year to year. Let's say one year each woman is entitled to one and eight-tenths green stamps. If a woman wants to have one child she can sell the eight-tenths to somebody else. If she wants two children, she has to enter the market and buy two-tenths more stamps. This could work in any country.