Objective:The main purpose of this study is to analyse the current situation and inequity status of children's medical security in China from the vision of children first.Methods:Using data from the China Family Panel Studies 2020 and based on the framework of universal health coverage cube,multivariate regression is used to analyse the differences in medical security between children and adults and among groups of children.Results:The participation rate of children in China is 80.96%,out-of-pocket ratios are 64.71%and 90.09%for inpatient and outpatient groups respectively.In terms of participation rate,insured children are less than that of adults(OR=0.434,P<0.01);within children's groups,attending school(OR=2.075,P<0.01)significantly increases children's participation rate,while left-behind by parent(s)(OR=0.791,P<0.05)significantly decrease children's participation rate.With respect to service and cost coverage,children have higher out-of-pocket ratios compared to adults(β=0.066,P<0.01);within children's groups,children eged 6 years and older have lower out-of-pocket medical expenses(β<-0.316,P<0.01),children with higher family income(β<-0.022,P<0.05),participated(β=-0.033,P<0.01),and hospitalized(β=-0.270,P<0.01)have lower out-of-pocket ratios.Conclusion:Double in equality exists in children's medical security in China.The level of children's health security in China is significantly lower than that of adults;within children's groups,children aged 0~5 years,not in school,left-behind by parent(s),and from lower-income families are more vulnerable.It is proposed to focus on increasing the participation rate of children through measures such as optimizing the contribution for children and launching family joint insurance.Policy design should also consider the needs of children and raise the level of children's benefits.Meanwhile,the focus should be on helping vulnerable groups in children,so as to ultimately achieve"children first"in health security.