Jessica Baker (born February 21, 1996) is the eighth child of the Baker family. Her and her twin sister Kim are the first set of fraternal twins in the Baker family.
In the first film she is seven years old and very close to her twin Kim. She is very smart and starts talking about algebra and math randomly. On her first day at the new school she is seen holding hands with Kim and Mark. When Jake, Mike and the school bullies get into a fight, Jessica tries to split them up. She is usually seen wearing the same outfit as her twin, although they are not identical. Sometimes she fights with Jake, especially when he stuck a bucket on her head, but they are still very close. She and Jake might fight but they still have a really close bond and care about each other deeply.
In the second film Jessica is nine years old and still very close to Kim. She readily goes on vacation with her family. When the siblings are all trying to defeat the packrat "Chisler", she is seen being lifted into the air by Kim whilst screaming. She takes part in the Labor Day Cup and participates in the egg toss with Kim, but the egg splatters all over her and she exclaims, "Ewwww..". When Nora has her baby Jesse comments and says "Wow that's a big baby...Too bad he wasn't there to help us win the cup". She and her brother Jake do not really fight like they used to. She was mad at her dad when he went to go spy on Sarah on her date with Eliot.Jessica Baker is played by Liliana Mumy in both films.