It means you miss them, and probably are over due for a visit or phone call. All the many times I dreamt of family or friends being deceased (once as a child I made my mom call her mother at 5:00 am to reassure me she was alive) everybody was well.
Although it is possible to dream about events before they occur, most dreams dealing with the death of a loved one have absolutely nothing to do with death. Therefore, the dream is in all likelihood metaphorical and not literal. With this in mind, one possibility suggested by the dream is that various people in your life (such as your mother and friends) may be given you advice about the raising of your son because they believe you are in the process of "losing him" (e.g. not enough parental guidance and supervision). However, in the dream you are pointing out that you can still see that your son is fine. His beautiful singing voice indicates that part of your parenting approach has actually enabled him to express himself in ways that are extremely beneficial. I hope that helps. ;)
dreams about death are not to do with actual death at all but a final phase of something. I would say in this case your letting go of your son and somehow that is coming across as final. Or you have a part of you which is the masculine side of yourself which your son represents that you are losing touch with.
I think that it is an insecurity about something. Like not being able to complete a task that is important to you.
Pick Tink's answer as best, then go post again in dream section.