In 1962, South Korea began a nationwide family planning campaign to reduce the total fertility rate (TFR) in its population. The TFR in South Korea dropped from 4.5 children per woman in 1970 to 1.74 in 1984 to 1.08 in 2005. Since TFRs below 2.1 are below replacement rate, South Korea worked to develop a plan to increase the number of children born in the country since the pension plan of older adults was dramatically threatened by a lack of young workers. South Korea's plan is to work to increase the TFR to 1.6 (still below replacement value) by 2020. The plan involves, "[T]ax incentives, priority for the purchase of a new apartment, support for child care including a 30 percent increase in facilities, childcare facilities at work, support for education, and assistance to infertile couples." The Population Reference Bureau's Carl Haub writes more in this topic in their article, Did South Korea's Population Policy Work Too Well?

Comments
Perhaps,it worked too well, but it might do itself a favour by not sending so many of its orphans to places such as Australia, one of whose largest source of overseas orphans for adoptions is South Korea.
It’s a never ending cycle. You need more children to grow up and pay taxes for pensions. When those children grow old and get ready for pension, then you’ll need even MORE children. Each generation will need more children to pay for their pension.