After the communist "land reform", the Chinese communist party / Chinese Government owns all the land in China. Now, local governments use land control and land sales as their major source of revenue. The end result is that vast majority of Chinese people live in small apartments, which are designed for 1 couple + 1 kid families. In big cities, average apartment size is around 60-80 sqm. In small cities, it could be 100-120 sqm. For a family of three kids to live in those small apartments, life is gonna be really tough.
Pardon me, but how is 100-120 sqm small? 60 sqm is small for 4 people yes, but everything else subject to how rooms are organized. We had 105 sqm growing up with 5 people and we had a very large living room + 4 bed rooms, no second bath room though.