I think the point is that we don’t specify how many children people can have at all. In addition to being ethically dubious, it has a high chance of backfiring as it had in China, and likely will be ineffective, as most population growth is currently relatively localized to a few areas of the world like the Middle East and Africa. Places like the US or Europe or East Asia have already largely stabilized population wise. What remains to be done is making the emissions per person sustainable, which isn’t true especially in the West. This in turn will make the technologies required for reducing emissions cheaper and more widespread for those countries that are still growing to utilize before their emissions per capital grows to that of current rich nations. Population control is a non-starter.