Although recent studies have established that children experience regret from around 6 years, we do not yet know when the ability to anticipate this emotion emerges, despite the importance of the anticipation of regret in decision-making. We examined whether children will anticipate they will feel regret if they were to find out in a box-choosing game that, had they made a different choice, they would have obtained a better prize. Experiment 1 replicated Guttentag and Ferrell’s study in which children were asked what they hoped was in a non-chosen box. Even 8- to 9-year olds find this question difficult. However, when asked what might make them feel sadder, 7- to 8-year olds (but not younger children) predicted that finding the larger prize in the unchosen box would make them feel this way. In Experiments 2 and 3, children predicted how they would feel if the unchosen box contained either a larger or smaller prize, in order to examine anticipation of both regret and of relief. Although 6- to 7-year olds do experience regret when they find out they could have won a better prize, they do not correctly anticipate feeling this way. By around 8 years, the majority of children are able to anticipate both regret and relief.