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.
Teddy tries warming up to her English teacher by having Charlie take part in her oral presentation on the book Animal Farm. Meanwhile, Gabe and his basketball team fire Bob as their coach and hire Amy instead, after winning their first game under her guidance. Also, PJ begins to spend way too much time with Amy's friends.
P.J.'s romance with Madison wreaks havoc on his friendship with Emmett as well as Bob and Amy marriage. Teddy agrees to help Gabe make peace with a bully at school.
PJ video tapes Charlie when she is being funny and puts the videos on the internet. Charlie becomes an over night super star getting tons of hits from the videos. When Amy and Bob find out, they don't like how Charlie is popular over the internet and they force PJ to take the videos down. After that, Charlie's fans get mad.
Spencer decides to help Teddy with her dance routine for the school talent show, but when he realizes she is terrible he fakes an injury to get out of it. Meanwhile, Jo convinces Gabe that she will help him win the class president election but instead she purposely sabotages him and runs for election herself.
Teddy needs money for a new cell phone and gets a job as the neighborhood dog walker, but the job is less than glamorous. After walking in PJ's job Kwikki Chikki, PJ gets jealous when his boss gives Teddy a job as the Kwikki Chikki spokesmodel. Teddy then comes up with a plan to get herself fired in order to give her brother the spotlight he deserves. Meanwhile, Amy sings a song with Charlie at her daycare which gets very competitive with the other mothers, while Gabe uses a mouse to play a trick on Bob.
Gabe is left in charge of Charlie while doing a school assignment with Jo. Meanwhile, Teddy accompanies a scared PJ to the dentist and Bob surprises Amy with a spa getaway.