Jessica Baker (born February 21, 1996) is the ninth 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.
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 Jessica comments and says "Wow that's a big baby...Too bad he wasn't there to help us win the cup".Jessica Baker is played by Liliana Mumy in both films.