This is a question a lot of parents ask, so it is important that you understand the philosophy behind an early treatment approach.
Starting treatment early can lower the risk of trauma to protruded upper front teeth and in severe cases improve aesthetics and self-esteem. In the majority of cases, early treatment can simplify and/or shorten the treatment length with fixed orthodontic appliances later (conventional braces as the third treatment stage), and avoid extraction of permanent teeth.