Just make human fertility longer. It's painfully short. Modern women are only really fertile for 25% of their life, and significant part of that period is spent on trying to become financially stable.

If women would be fertile up to 60, which is also something reasonable for almost every other mammal, we would be swimming in children even in developed countries and will have much more severe issues with overpopulation :)

Currently there is a huge evolutionary pressure towards having longer fertility period so it is bound to arrive in some quantity anyway.