What factors may affect a preschooler's emotional development?

Emotions. The love, understanding, attentiveness and empathy they receive is crucial to a young child's development. You may benefit from reading my blog, "the psychology of goodness" on the soundmindz.Org website which describes how early emotional development influences us in one direction or the other. Best.
Several levels. Just to name a few basic, key factors: genetic predispositions would be a big one, i.e. Certain characterological traits passed on from parent to child; 2) both parents' consistency of empathy, patience, and understanding towards the child; 3) stability of the home environment; 4) quality of the community outside of the home, i.e. Preschool teachers' skill level, friendship development, etc.