This research examines adults', and for the first time, children's and adolescents' reaction to being ostracized and included, using an on-line game, ‘Cyberball’ with same and opposite sex players. Ostracism strongly threatened four primary needs (esteem, belonging, meaning, and control) and lowered mood among 8- to 9-year-olds, 13- to 14-year-olds, and adults. However, it did so in different ways. Ostracism threatened self-esteem needs more among 8- to 9-year-olds than older participants. Among 13- to 14-year-olds, ostracism threatened belonging more than other needs. Belonging was threatened most when ostracism was participants' first experience in the game. Moreover, when participants had been included beforehand, ostracism threatened meaning needs most strongly. Gender of other players had no effect. Practical and developmental implications for social inclusion and on-line experiences among children and young people are discussed.