Big Bro Theodore is an episode of the ALVINNN!!! and The Chipmunks series.
When Theodore mistakenly thinks he's the oldest brother, he tries to be a better role model for Alvin and Simon.
Alvin tries to get out of playing hide-and-seek with Theodore though a voice recording of Alvin reveals he promised to play the game whenever his younger brother wanted. While Alvin counts and Theodore hides, Theodore overhears Dave talking on the phone about summer camp and how he's the oldest. Alvin finds him in the open and Theo agrees that the game is for little kids. In an effort to be a better big brother, the green-clad chipmunk researches what he should be doing for his younger siblings. Simon walks in on him, causing him to fluster, before attempting to assist Simon with his calculus homework. Later that night, Alvin is startled to find Theodore in his bed waiting to read him a bedtime story. Theodore talks himself to sleep and Alvin and Simon discover Theo wants to be a big brother. Simon suggests this could be an important growing stage for their brother (Alvin's first thought is that Dave's having a baby) and they should play along. Alvin does his best to let Theodore take care of him, but when he hits his breaking point after spending the afternoon in a trash can, Alvin wants to tell Theodore the truth though Simon disagrees. Instead, to protect their brother's self-confidence, Simon recommends making Theodore want to be their younger brother again. Alvin rushes to Theodore claiming there are ghost eyes in the basement and he's too scared to go down and get his sweatshirt. Theodore reluctantly travels down the stairs but runs into Dave screaming once Alvin throws a pencil into the basement. Theodore explains to Dave that he was trying to be the big brother, only that he's not cut out to be. Dave clarifies the confusion of his call and Theodore excitedly jumps into the trash bin for the chocolate bar he took from Alvin and threw away when he was setting a good example.
- "Follow Me" 
- In the book Theodore reads to Alvin, the character pictured resembles Stuart Little.
- This episode firmly confirms that Alvin is indeed the middle child, and Simon indeed being the eldest, within the series. This was first implied in The Sub when Alvin states to Dave "you're not very nice to the middle child."
- Camp Unasakawakaka from the season two Summer Camp is mentioned in the episode.