Recent research suggests that infants prefer prosocial behaviour. However, some studies have failed to report this preference, raising the question of which specific parameters allow it to be observed. We attempted to answer this question by investigating whether the preference varies (1) with age (by testing infants aged 6, 12 and 18 months), (2) with type of social behaviour (help, play or share) and (3) when the pro- and antisocial agents' appearance is manipulated (neutral, own-race or other-race faces). To this end, we use an eye-tracking methodology to assess infants' preferences for pro- versus antisocial agents featured in animated cartoons. We found that the prosocial preference was not stable across ages and varied according to social scenario. No sound conclusion could be reached about the influence of faces. Our results raise a new question, concerning the extent to which very young infants perceive prosociality in complex social behaviour.