Cecil Willson is Rebecca Willson's smart twin brother and Maria's older half-brother who has a contentious relationship with his step-mother, Marissa Wilson. His dad is Wilbur Wilson. When Marissa leaves a necklace that The Timekeeper wants from Rebecca, Cecil and his sister team up with their step-cousins Juni and Carmen to save their step-mother.
Spy Kids 4: All the Time in the World
- He can't really hear very well and uses hearing aids, and that has increased his senses of smell.
- He also takes from Wilbur because he wants to be a spy hunter.
- He is shown to be left-handed in a deleted scene.
- Cecil likes to eat junk food including cheese puffs, candy, and cereal.
- He can really fight with his Hammer Hands and he even knows anagrams and can get access by unscrambling letters to anything that can't be unlocked as he learned it from video games.
- He owns a Nintendo DSI.
- Rebecca sometimes punches him in the arm and he says "ouch".
- Cecil is bullied by a kid who makes him do his homework.
- It is currently unknown what the age gap between Rebecca and Cecil is. Whether Cecil is the older twin or the younger twin, it has not yet been confirmed.