I study human survival, so I have been working on this problem. I think I know what the issue is and a practical, economical solution that will solve other problems as well. I wull put below this an abstract I wrote before the last re-write cycle, so it isn't polished, but it should give an idea of what I am looking at.

For a variety of reasons, there is a decline in population in developed countries. My previous work was a survey that listed 35 reasons this might occur. The most obvious reasons and most commonly considered is the high cost of raising a family as well as concern about the future. More reasons can be provided by philosophy and particularly by biology. Quite notably and critically, humans do not have a great deal of instinct to have families. They do have a strong instinct to have sex though and that leads to babies and releases nurturing behaviors. After all those reasons are evaluated, two problems remain. What can be done about it? That will be discussed and there are a number of things. The other problem is that it feels like there is another missing factor related to either moral instinct, survival instinct or both. Most likely the neurological mechanisms behind moral instinct are not being well developed largely due to moral education being relegated to culture. We do not have the moral character to make the moral decision to have families. I see problems with that theory as there is a lot of morality taught by culture, that is, modern entertainment. I don't have enough data though to be sure. The attraction of that theory though is in two parts, particularly that it would be easy to address. Reason 1 is the overarching moral context common to humans through history. Admitting my biases, I always try to understand that. Yes, I am a doctor looking for my favorite disease, but I also have a pretty good understanding of that disease and its possible symptoms. Reason 2 is that there should be a solution to it that, by the way, has many potential beneficial side effects. Teach children philosophy like it was taught before philosophy became a casualty of the war between science and religion. It shouldn't matter a whole too much which philosophy you teach though thought should be put into it. (Do not teach existentialism!) All philosophies have moral components that should do the job. It should be like lifting weights. You will get physical development regardless of what weights you are lifting. The purpose is to develop the neural net that is somewhat specialized for moral behavior, by the teaching of philosophy and it attendant morality. Hopefully the survival instinct isn't critical to this, but that is another question.