I think there are some pretty good resources on the net about what to do about nervous flyers, including children. I think maybe it's the same principle.
At early teenage years, I think some children would take well to being shown how many cruise ships there are on the seas at any one time and how many go off week after week, year after year without incident. Maybe also an explanation that after an incident like this, if anything, travel is safer.
The reality is that going on a cruise is safer than riding a bicycle, statistically, I would guess. While this would not be much solace for a 7-year old, I think it might be one approach for a pre-teen, depending on the child. By that age, the child knows that there are risks in life and can be educated about the difference between taking careless risks and taking calculated risks, like flying in an airplane, or going on a cruise.
Most every child has anxieties. Some are fleeting -- like those caused by seeing a scary movie, or news of a shipping disaster, or monster-in-the-closet fantasies. Some people, though, really do have anxiety disorders (including, of course, children). If anxieties are more than one-off random things and actually interfere with life, or are accompanied by other anxiety symptoms or OCD symptoms, consulting with your pediatrician to see whether a visit to a professional who is versed in these issues is something to consider. People with anxiety disorders are really suffering, and the tough part of it is that they don't even know, because they don't have a baseline to compare it to. We all know what it feels like when our finger isn't broken, so when it's broken, we know to go the doctor.
Then, of course, there is the matter that sometimes kids just don't want what their parents want, irrespective of anxiety. I find disney vacations require careful analysis and honesty about whether I'm doing it for me or for them.