Honestly I included both because I wanted to include people who elect not to have children. Currently, the child credits are in place to strong arm people into having children, and there is no upper bound on the number of children it covers. This can really be a financial impediment for people who either have chosen not to have children or have not been able to. Conversely, families who elect to have an arbitrarily large number of children end up placing a disproportionately larger burden on social infrastructure. They elevate the load on schools more than other families, they consume more food than other families, etc. By tuning the how the parameter is calculated you can provide some refund for having no children, increase it to a point for small numbers, then level off or even reverse it as the number increases. Thus this provides some economic benefit for people making the very ecologically and financially rational decision not to have children, still helps ease the financial burden for people who have small numbers of children, and holds people who incur a higher social burden by their decision have many children. I am specifically leaving out numbers on these as the moral and ethical decisions of what constitutes 'few' and 'many' for this discussion are something that can and should be actively debated to determine the social validity. Also, it could be done in a way which would allow the tuning to be adjusted based on social needs for population growth.