It already has. Thats why its 36 years with "1 child" and only 6 years with "2 child" before it went to "3 child", they're deep in deficit and are trying to catch up.
Further the new "3 child" policy isn't just a passive allowance. The government of China is actively incentivizing parents to have children.
"An extra month off and $80 monthly stipends and 30-day days of additional leave part of a series of sweetners local governments have unveiled as China kicks off the legislative process to allow married couples to have a third child in a drive to curb a precipitous decline in births." source