They stopped the one child policy nine years ago; they had it in the first place because demographic projections had them severely overpopulated if they didn't.

During the period in which it was active, their GDP increased by a factor of about 62. Not percentage, multiple.

They reversed the policy too late. Their rapid growth was them seizing the low hanging fruit upgrading from a country of almost entirely peasants to slightly fewer peasants, all funded by Western greed. Those gains will never happen again.