Why does women in Japan act like a child sometimes?
The question has been puzzling me a long time. Adult women in Japan have cute stuffed animals in 
their home (so many!) , they prefer to wear sometimes girlish clothes, or behave like a child in public. And they love cute things. Japanese advertisement industry has proven that.
Someone once explained this to me with a most easy way; the reason is that the women who are now adults were grown in era of economical well fare. During their childhood they were going through the bunch of hard examinations, prepschools and university entrance exams, while they were supported by their parents and entire family. Who could success through in this trial and enter the famous universities, sometimes avoided the trial of life that leads person to become independent.
This pressure of success that family experiences in Japan, is not to be underestimated. Still now, most of the major Japanese companies tend to hire graduates of famous universities, regardless of the level of actual knowledge. This partly explains why parents support their children in such way that feels overprotective for westerners. In some cases however parents have bought the children anything she wants and provided the wrong kind of support.
It should be also noted that Japanese children traditionally live at home until they get married. This is veryunderstandable because of high expenses of rent and living in Japan. However since most of them never experience living alone, shifting directly from home to married life, they sometimes cannot get totally self supporting. After finishing the schools many of them start to do work from home, earning quite large sums of money what they then spend as they please. The lack of independency has said to cause problems for marriage life later. In western world, this problem is often avoided since children often move to live by their own while studying in the university.
Women might also feel reluctant changing the male-dominant society, feeling comfort from relying on men. Aside that, men seem to be attracted by traditionally cute and soft Japanese females. However there are clear signs that this is changing now. The new generation of girls seem to be more independent.
I believe that adult women continue to use the front cortex of the brain for thinking the same as children do. This part also activates emotions. Men use the frontal lobes(usually but there are men who still think like children e.g Boris Johnson, Mayor of London)