Eddie Neutron, better known as Baby Eddie, is Jimmy's evil 17½-month-old cousin and Newt and Kari's son with a grown man's voice.
Eddie is mean, evil, ruthless, selfish, sadistic and greedy. He believes he is a lot smarter than Jimmy. When there are adults around, just when he talks in his normal voice, he then suddenly talks in a baby voice and says, "Goo!", feigning innocence. He was plotting to do away with the entire clan so he could get Amanda's amazing wealth.
Despite his intelligence and adult voice, he is still mentally immature as he is physically. He cries when he is upset, he threw a fit when Jimmy destroyed his rattle, demands his cup, and always demands a diaper change from peers and others. He always smells and has a full diaper on.
- Eddie's attitude and behavior is quite similar to Chucky from the Child's Play franchise.
- Since he is trapped in the dinosaur times, it is most likely that he was either eaten by one of the dinosaurs or has managed to scare them off with his dirty diaper.
- He flirted with Beautiful Gorgeous in "The League of Villains," but she never returned the interest.
- Eddie is similar in terms of behavior to Stewie Griffin from Family Guy as both are evil, are a year old, and have the ability to talk and walk.
- He resembles Granny Neutron as an infant, as seen in "Granny Baby".
- Eddie is the only villain to be related to any of the main characters.
Main Characters: Jimmy Neutron | Carl Wheezer | Sheen Estevez | Nick Dean | Cindy Vortex | Libby Folfax | Brittany Tenelli | Betty Quinlan | Goddard