Many theory of mind researchers have argued that even preschoolers understand the causal relationship between desires and emotions: the fulfilment of a desire results in a positive emotion, whereas its frustration elicits a negative emotion. Children can acknowledge this simple link between desires and emotions, even when their own desire differs from that of the story protagonist. However, in this paper we argue that under some conditions preschool children will not base their emotion predictions for another person on the basis of the other person's desires. In the first experiment, 3-to 5-year-old children were tested for their understanding of desires, when the protagonist's desire for a snack increasingly conflicted with their own preference for a snack. Only the 4-year-olds performed as expected: they gave more accurate emotion predictions when the distance between their own preference and the protagonist's desire was reduced. When the snacks were replaced by toys, however, preschool children showed a bias in their emotion predictions that seemed gender related. The second experiment confirmed that sex-stereotyped beliefs about desirability biased children's predictions of others' emotions: 4- and 5-year-old children were more accurate in their predictions when the protagonist had a traditional desire (a girl wanting to play with a doll), than when the protagonist had a non-traditional desire (a boy wanting to play with a doll), irrespective of children's own preferences for one toy over the other. In sum, evidence was found for two biasing influences in children's understanding of others' emotions: (1) an increased distance between the protagonist's desire and participants' own desires, and (2) beliefs about desirability based on, for example, cultural-norms for gender related preferences, which increases with age.