The brain develops the connections according to what it experiences in those formative early years - those experiences are in the context of relationships. If your environment is one of violence and aggression, most likely the 'fight or flight' response will be overly developed. You will be more likely to over-react to situations of stress, and use aggression or violence.
One day, hopefully many decades from now, I can picture myself rocking manically in an old folks' home (or mental asylum), still haunted by the sinking realisation that the the Wheels On The Bus may never stop going round and round. Or that the Grand Old Duke of York will never stop marching his troops to the top of the hill. Or that I will be Row, Row, Rowing My Boat gently down the stream until i'm clinically insane.