The Duncans a European-American family in Colorado is adjusting to the surprise birth of their fourth child, Charlie. When parents Amy and Bob return to work they put their latest addition in the care of her three older siblings, PJ, Teddy, and Gabe. Teens PJ and Teddy and tween brother Gabe are typical kids -- that is, until their mother has another baby. The arrival of their new sister completely upends the entire household. When their mother heads back to work after Charlie's birth, it's up to the kids and their dad to keep the home fires burning -- and to keep Charlie out of trouble as she learns to sit up, crawl, walk and run. Teddy, as the older sister, makes a personalized video diary for Charlie, in each episode adding a nugget of wisdom for her baby sibling.
A puzzled P.J. and Teddy cannot understand why their friends are angry with them, until the monthly cell phone bill arrives.
The family reminisces about the day Charlie was born.
Teddy and P.J. hatch a plan to keep Bob from tearing down their cherished childhood tree house.
Teddy tries to strike up a friendship her Uncle Mel after Bob refuses to tell her why he wants nothing to do with him. P.J. and Gabe plan to turn Charlie into a model behind Amy's back.
PJ meets a girl who has an unexpected link to Bob. Emmett is upset that PJ isn't prioritising him. Gabe is bullied by a girl at school.
Gabe gets his first crush on a girl named Kit, he then lies to her so they can have something in common. Meanwhile, Mrs. Dabney asks Teddy to catsit her cat Kaboodle and Teddy thinks the cat is sick because she just lying around. PJ uses Charlie to make more money on deliveries by saying he is watching her while his mom at the hospital, not mentioning she actually works there.