Several studies have indicated only a modest concordance of attachment security in siblings in infancy. Until now, very little was known about the concordance of siblings’ attachment security beyond infancy, as assessed by the attachment story completion task. This cross-sectional study aims to examine the concordance of attachment representations of 38 first-born (4–7 years) and 38 second-born (3–5 years) siblings living in middle-class two-parent families. Personality factors and the level of parenting stress of the biological mothers (30–43 years) were analysed in relation to children’s attachment security. The results indicate a 43 % secure-insecure concordance rate between siblings’ attachment representations. Sibling’s gender correspondence, age differences and differences in parenting stress were not related to attachment concordance whereas gender of the first-born child was related to attachment concordance. The results also indicate that older children more frequently had secure attachment representations compared to younger children and that attachment insecurity was associated with greater negative impacts of life events, lower maternal life satisfaction and higher parenting stress. Our study indicates that siblings’ attachment representations may lack concordance even when siblings are assessed by the same method at the same time. If maternal and environmental factors are able to explain a substantial amount of variance in the attachment security of individual children, non-shared environmental factors might be underestimated when studying siblings’ attachment representations. The significant effect of age on children’s attachment representations found in this study suggests the need for future research on the stability of attachment representations during the preschool years.