The Japanese government has never had a "one-child" policy.
Indeed, the Japanese government at all levels positively encourages people to have children; the problem in Japan is that children are a very, very expensive proposition, not that the government thinks that there are too many.
It wasn’t called “one-child.” In the late 60s, they did indeed promote child-reduction with birth-control and abortion. We saw the results in the 80s when Japanese industries and even department stores were relying on specialized robots in an attempt to replace the missing labor pool.
You’re quite right though. NOW Japan IS encouraging childbirth, but it’s BECAUSE of their earlier policy.