DCL is extremely cautious regarding ANY vomiting or diarrhea reported to them. Their main issue is to avoid infecting a ship full of passengers. The reason is that they do not want to have to report an outbreak of the Novovirus or any other GI illness; other cruise lines have hit reporting levels, DCL never has. The ship must report to the US health authorities if 3% of the ship's population becomes ill. In US schools, reporting is not required until 10% of the population is absent.
A few comments. The "common cold" does not cause vomiting. One can vomit due to mucous in the throat, coughing, etc. but the "common cold" is a rhinovirus which does not cause vomiting. Bottom line, this poster does not know why the DD vomited. DCL can deny boarding for any reason. The mother could have demanded that the child be seen by the ship's doctor, but the result would have been the same. Their policy is to deny boarding to anyone they suspect may be ill at embarkation. When I was boarding with 5 teens, I threatened them within an inch of their lives if anyone joked around about illnesses telling them that it could mean no cruising. Why would then joke around? For the same reason they tell the Customs inspector that they have a pet bird in their suitcase--just plain nuisance value! "But mom, he KNEW we were joking."