Do you think that there should be more young people produced now to look after the old? Because if you do, that is a short term view. Kicking it down the road, as several pps have said.
The idea behind any temp boost in children numbers is to have a slump not a cliff drop in population - so a slower decline.
Long term I don't think anyone is asking for endless population increases.
I think everywhere but few countries in Africa is predicted to go below replacement figures fairly soon meaning a drop across most populations - so there's worry even immigration may not be enough to prop up some countries with low birth rates.
Apparently the prediction are now that 2025 in UK will see first natural population decline more deaths than births but immigration mean population will still increase mitigating affects and kicking them down the road.
https://www.ft.com/content/7a558711-c1b8-4a41-8e72-8470cbd117e5