Friendships are crucial to children's socioemotional development and quality of life. Children born preterm (<37 weeks gestation) have an increased risk for social relationship difficulties, including fewer friends, but the mechanisms underlying the link between lower gestational age and fewer friendships are not clear. The prospective Bavarian Longitudinal Study investigated potential cascading effects on N = 1,181 children's friendships at 8 years. Path modelling indicated that higher gestational age predicted good early parent–infant relationship quality, good inhibitory control, and higher friendship scores. Good parent–infant relationship quality predicted good inhibitory control, which subsequently predicted low social inhibition at 6 years and higher friendship scores at 8 years. There is evidence of cascading effects from gestational age to early parent–infant relationships, to toddlers' inhibitory control, and to social inhibition, which partially explain differences in children's friendships at 8 years of age. Highlights: Preterm children are at risk for social problems and fewer friends, but the mechanisms underlying this risk are not known. Path modelling showed that gestational age predicted good early parent–infant relationship and inhibitory control, which subsequently predicted low social inhibition and higher friendship scores. Cascading effects from gestational age to parent–infant relationships, to inhibitory control, and to social inhibition partially explain differences in friendships at 8 years.