Xavier is one of Candace Flynn's future children. He was voiced by Noah Munck.
He and his brother Fred are generally rather inactive, and constantly like to make note on how they're just sitting in front of the digital tree in their family's backyard, much to the annoyance of their sister Amanda. Their life takes a turning point, though, when they by chance get a visit from the younger-aged versions of their uncles, Ferb. After the aforementioned visit, Xavier and Fred construct bumper cars that can move in five dimensions, but they still answer Amanda's query about their activities with "Nothing" ("Quantum Boogaloo").
Xavier and Fred are as bright and creative, and build impossible stuff just like Phineas and Ferb, although it took the younger version of their uncles to bring it out of them.
Xavier has bright blue eyes and blond hair, which gives him an appearance similar to his presumable father, Jeremy Johnson.
- "Amanda" and "Xavier" are the two names that Candace had picked out for her future children. Given her interest in Jeremy, it's possible that he is the father of both children. However, this is not definitive.
- His, Fred's, and Amanda's situation is analogous to Phineas, Ferb's, and Candace's except rather than trying to "bust" her brothers for doing something, Amanda tries to bust Xavier and Fred for doing nothing. This being the case, Xavier is the Phineas of the pair as he talks more and he even tells that Fred that he likes Phineas while Fred responds that he likes Ferb.
- If Jeremy Johnson is Xavier's father, that would mean Suzy Johnson would be his aunt. He would be more distantly related to Nicolette too (Jeremy's cousin) from "Plane!".
- In the Dutch version of Phineas and Ferb, Xavier is voiced by the winner of the Junior Eurovision Song Contest 2009], Ralf Mackenbach.