Abstract Background In Luxembourg, despite its economic prosperity, 28.6 % of children are estimated to be at the risk of poverty. Research has shown that growing up with socioeconomic disadvantage is associated with worse physical and mental health in childhood. We explore the association of socioeconomic status with health, health behaviours and access to healthcare in Luxembourg for children up to age twelve. Methods We used data from 2014 to 2022 for 11-12 year old children from the Health Behaviour in School-aged Children (HBSC) survey as well as social security data from Luxembourg for a similar time period and children 0 to 12 years old. To assess socioeconomic status, we used information on self-perceived household wealth for the HBSC results and stratified health and health behaviours by well-off, average, or less well-off households. For the social security data, we stratified access to care indicators by equivalized household income quintiles. Results We found that physical activity levels, nutritional quality and daily routines such as eating breakfast and brushing teeth are significantly lower in children from less affluent families. For example, 61% of 11-12-year-old children from well-off families reported eating breakfast every day, but only 41% of children from less well-off families. Only 23% of 11-12 year olds from less affluent families rated their health as excellent, compared to 52% of children from affluent families. There were similarly large differences for multiple health complaints, with 63% of children from less affluent families reporting this indicator for psychosomatic problems, compared to 34% of children from affluent families. We did not find differences in the use of pre- and postnatal care visits. Conclusions Socioeconomic differences in child health, mental health and health behaviours are large, with children from poorer households being in worse physical and mental health and less likely to report positive health behaviours. Key messages • Many children in Luxembourg face socioeconomic challenges that are adversely associated with health and health behaviours. The underlying reasons require further attention to improve child health. • Children from poorer backgrounds are in significantly worse mental health than children from better off families in Luxembourg.