Japan is now a threat to the loss of human population, the reason as you say, if we think in a common sense, children are not a burden on the economy, precisely without realizing those who do not have children that is the economic burden, life is sometimes strange, that's the situation.
I have seen some people without children, they are burdens with themselves, when they suffer from illness, no one cares about them until the old man dies without guiding, For me the child is a sustenance carrier for those who care for him, raising him sincerely, many children who return the favor to their parents, Whether it's from the economic or physical side, children are not a problem for the lives of parents while being educated wisely.
Everything that has merit also has demerits. A high population could be a burden to the economy since there will be pressure on infrastructure and government spending. But a high population is also an industrial and military strength of countries. Both Japan and China are trying to reverse their birth rate restriction policies because it is becoming a national emergency, since the majority of the population is aging and the birth rate is low.
In rich nations, they have a well-financed welfare system for the elderly. Retirees and the elderly depend on the government for survival. The perception of relying on children at an old age is popular in developing countries that have poor economic conditions.