The answer to this, of course, depends on the degree to which children of that age watch TV. It also depends on what they watch.
For many preschoolers, the kind of TV they are allowed to watch is explicitly meant to socialize. When children watch Barney or Dora the Explorer, for example, they are being taught specific social values. They are being taught to share and to be kind to others. They are being taught to care about the environment. These shows are quite explicit in telling children that these are the proper ways in which to behave.
If preschoolers watch other shows, they may be socialized less explicitly. They may watch shows that have a great deal of violence in them, for example. These shows may socialize them to believe that violence is an acceptable way to deal with one’s problems. They may see shows that portray girls or women in subordinate positions. These will teach them that our society sees men as more important than women. These shows are not explicitly trying to teach those things, but kids who see such shows often enough will internalize those ideas.
Thus, the kind of socialization kids get from TV depends on the shows they watch and how often they watch those shows.