 The aim of this study is to carry out a double-blind placebo controlled trial of sertraline in children with ASD who are between the ages of 2 years and 5 years old inclusive. At baseline, the researchers will assess behavioral and cognitive development. Each participant will be involved in this trial for a period of six months. This will include three visits to the UC Davis MIND Institute and eight phone calls. The researchers will also assess the side effects of the sertraline treatment throughout the study. 