More children, more blessings? The effect of children on depression symptom in old age

China has entered a stage of deep population aging, and it has brought great challenges to the country and society. With the aggravation of aging, the physical and mental health problems of the old adults and the subsequent elderly-care problems have been concerned by all sectors of society. With the development of economy and society and the change of fertility concept, especially in recent years, after the change of the fertility policy, whether the number of children has a protective effect on the mental health of the old adults has been widely concerned by the society. This study using the Chinese health and retirement longitudinal study (CHARLS) data, established instrument variable regression models with an instrument variable chosen according with the Chinese fertility preference, and then deeply analyzed the causal effect of the number of children on the depressive symptoms of the old adults.The results of the study showed that, (1) Chinese people had a common fertility preference for boys; (2) and the fertility preference for boys was quite steady among generations. (3) The Naïve Probit regression indicated that, the number of children could significantly increase depressive symptoms in old age, however, the regression of instrumental variable showed that the number of children had no significant effect on the depressive symptoms in old age.Using CHARLS 2018 data, and also using an instrument variable regression, this study made a series of classification analysis according to the respondents’ factors like age, gender, marital status, places of residence (urban or rural areas), and education levels, and moreover, we used the data of CHARLS 2011 made the stability test, and all the results were consistent. This study illustrated that to improve depressive symptoms in older adults by increasing the number of children only was not feasible, and these conclusions will provide theoretical reference for the management of depression status in the old age and the social care for the old adults in China.