If you have to cancel an outing or a vacation, you could explain that disappointments are part of life and perhaps discuss how you deal with such disappointments.
وإذا اضطررت ان تلغي نزهة او عطلة ،‏ فأفهمه ان الشخص لا ينال كل ما يتمناه في الدنيا ،‏ واشرح له ماذا تفعل انت حين يحصل ذلك معك .‏