The series centers on the Duncan family, who are still adjusting to the surprise birth of their fourth child, Charlie. When parents Amy, a nurse, and Bob, an exterminator, return to work, they ask their 3 older children (teens PJ & Teddy, and 10 year-old Gabe) for help raising their little sister. The events of each episode become material for a video diary Teddy is making for her younger sister.