Evidence suggests that departures from pure self-interest are due, at least partly, to individuals conditioning their behaviour on the perceived intentions of others. We present a new experiment that refines the study of intention-based other-regarding motives. Using a series of mini-ultimatum games that have been extensively studied in the literature, we compare the behaviour of normally-developing (ND) children to that of children with Autism Spectrum Disorder (ASD), who typically lack the ability to attribute intentions to the observed actions of others. We find that ND children’s rejection behaviour responds systematically to changes in the set of available options, in line with previous findings. ASD children’s rejections are virtually unaffected by the intentions that could be inferred from the games’ strategy space. These differences are mainly driven by ASD children with low mentalising abilities.