I find all the reasoning about culture and spending habits in this thread to be lazy thinking. If it were as simple as banning some things, then every country would have done it already.
You are having trouble reasoning why higher average income countries have a lower fertility rate than lower average income countries. A simple reason for this is that the income expectations for a child scales with the parent's income. That is to say the higher income country has higher expectations for a child than the lower income country.
GDP per Capita (because average income data is inconsistent/poor/non-existent for some of the countries):
Vietnam: 2,785 USD
Malaysia: 10,401 USD
Indonesia: 3,869 USD
Philippines: 3,298 USD
China: 10,500 USD
Shanghai: 22,560 USD
Beijing: 23,908 USD
Guangdong: 20,887 USD (126,012,510 people)
Let's suppose that income is correlated to GDP per Capita. That is to say the average child born in Guangdong province right now is expected to produce on average 7 times more than the average child born in Vietnam. Even if Vietnam's GDP per Capita doubled to ~5,600 USD and so did income, then it would still be just a bit over a quarter of Guangdong province's GDP per Capita. To increase a child's future productivity more resources/money needs to be invested in the child (aka increasing the cost of raising a child). That is to say increasing living standards also increases the cost of raising a child. So raising a child in a low income country is no longer totally comparable to raising a child in a high income country.
A naive solution is to just consume more resources/money per child (aka have the government or parents spend more money on children). But one quickly realizes that there are physical resources limits such as limited farmland, limited natural resources, excessive pollution due to industrialization, climate change, limited school slots, limited jobs, etc. Of course such limits are not absolute and technology can help increase these limits. For example, the Green Revolution (great increase in production of food grains in developing countries) in the 1950s and 1960s corresponded with a massive baby boom. But there is also no guarantees that a society can sustainably increase resource limits to match an increased population and improved living standards.
Having said all that is demographic decline permanant? Nope. The most famous is example of this is France. In 1907 France's population peaked at 40,400,000 and dropped to a low of 38,500,000 in 1920. It was not until ~20 years later in 1929 that the population returned to 40,500,000. Today France's population is 65,200,000 and this was in large part due to the 1950s and 1960s. So the lessons from this scenario are:
(1) Demographic trends take decades to change. There are no quick and easy solutions and scapegoats to demographics like some people in this thread want.
(2) Nobody in 1907 France could/would have predicated the 1950s and 1960s baby boom. Sometimes the future changes to demographics are outside the control of the government and simply unpredictable.