Previous studies suggest that generous norms influence sharing behaviour from middle childhood onwards. However, no previous study has assessed how these norms could change prior sharing decisions and beliefs about others' sharing behaviour and whether such beliefs may be linked to behavioural change promoted by generous norms. Through a within-subject design, we evaluate 4-to-9-year-old children (N = 111) using two dictator games
one as baseline and the other after being exposed to either a generous or a selfish descriptive norm. Similar to previous studies, the generous norm increased baseline sharing decisions only in children older than 7. In this age group, decisions and beliefs were significantly associated after this norm. Lastly, only the generous norm and not the selfish norm increased expectations about others' sharing behaviour in both age groups. These results suggest that expectations about others' sharing behaviour may support the development of more cooperative sharing behaviour. At least through descriptive norms, it appears more challenging to nudge children to share less and to believe that most children would share selfishly.