From a professional perspective (I'm a psychologist), if your children tend to be anxious, a surprise cruise might be overwhelming for them. Parents always have good intentions when surprising their kids but are often not met with the reaction they hoped for; this is particularly true for children who have anxiety. In addition, kids can exhibit behavioral difficulties bc they are overwhelmed and anxious and have difficulty articulating their fears/worries. Big trips and new experiences tend to be more successful if children know what to expect and have the opportunity to process the information.