It's a question many couples wrestle with – how many children should you have? 

Well, if happiness is your goal, a study suggests the answer is two, and ideally both girls.

Researchers have found that having only daughters was positively associated with parental happiness.

In particular, parents with two girls – such as the Obamas, and Ryan Gosling and Eva Mendes – reported the highest levels of happiness.

‘There are significant differences in the association between the gender composition of offspring and happiness, with a “daughter advantage” emerging,’ the researchers said.

The scientists from Zhejiang Gongshang University analysed previous surveys in China to understand the link between offspring and parental happiness.

They used six waves of the Chinese General Social Survey – a survey carried out from 2012 to 2021 that included a total of 49,752 families. 

It included questions on happiness, parenthood, number of children and the gender composition of the offspring.

The happiest couples appeared to be those in middle-age with only daughters – and ideally two of them. 

As for why this is the case, the researchers have two leading theories. 

First, they point to the gender role theory. This suggests that social norms and upbringing influence how men and women express emotions and build relationships. 

'Women are socialised to be more emotionally expressive, empathetic, and oriented toward interpersonal connection, whereas men are socialized toward instrumentality and emotional restraint,' the researchers explained in their study, published in Acta Psychologica. 

Next, the researchers highlight the concept of 'kinkeeping' – the work of maintaining family ties and emotional bonds across generations. 

'[This] has been shown to be disproportionately performed by women, particularly daughters,' they added. 

'In the context of parent–child relationships, daughters are more likely to initiate contact, provide emotional support, and serve as confidantes to ageing parents.'

The researchers point out that this study focused solely on people living in China, and say the findings may vary in other countries. 

They added: 'These findings deepen our understanding of how family size is associated with the quality of life of individuals and, in particular, provide empirical evidence for understanding the patterns and correlates of Chinese families' pursuit of happiness in the context of institutional change, cultural norms, and individual choices.'