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.
Gabe's friends come over for a sleepover. Meanwhile, Teddy prepares for an important role in school play and Charlie refuses to sleep in her first "big girl" bed.
Charlie bites Teddy's boyfriend, Spencer. Teddy then discovers that he has another girlfriend, Skylar (Samantha Boscarino) when she tries to smooth things out at Spencer's job. Skylar also finds out and she and Teddy dump Spencer. Meanwhile, Gabe treats PJ like a personal chauffeur because he lent PJ money to buy a car. PJ tells Gabe he could have the car because the car was supposedly haunted, but was just a scheme to scare Gabe into letting PJ have his car.
Teddy starts a rock band with Skylar and wrote a mean song about Spencer. Meanwhile, Gabe and PJ are tired of sharing the same room, so Gabe sleeps in an extra room in Mrs. Dabney's house. Amy uses the free day care at a gym to go to a spa down the street.
A new kid on the block named Austin (Nathan Gamble) who Gabe is forced to become friends with develops a crush on Teddy. She uses the crush to her advantage to make Spencer jealous, who has already gotten a new girlfriend. Meanwhile, Bob temporarily fills in as a member of PJ's band after Charlie gets their newest member sick.
Gabe tricks Amy and Bob into getting him a new bike.
The Duncans go on a family road trip to a ski resort in the mountains. While on the ski trip, Teddy meets a psychic who tells her that she will meet her true love during the vacation. She meets two guys, and her ex-boyfriend, Spencer. What will happen next?