Baby Theo is the class bird, who has failed to hatch for an extended period of time, much to the worry of Gwyn Sanders, his most obsessive caretaker. In the episode "Chick Magnet", Theo planned on helping her by causing him to hatch. He invented a radioactive lightbulb, which he used to speed up the growth process of the chick. Gwyn was overjoyed, once the chick hatched and named it "Baby Theo", unknowingly naming him after Theo, whose name she mistook for "Tywin".
Theo and Gwyn took care of Baby Theo throughout the school day and Theo treated him as though he were her son, pretending to be married to Gwyn. Baby Theo was adored and stared at in awe, by every other student and teacher in the school. After only 16 minutes of it's life, Baby Theo had instantly learned how to walk, priding Theo and concerning Gwyn.
Theo cared so much for Baby Theo, that he feared Gwyn's neglegence and got on her every nerve, correcting her poor parenting. Meanwhile, Baby Theo only grew more in size, and attachment to Theo.
When Principal Applecrab announced Gwyn, Theo, and Baby Theo as the family of the year Baby Theo had reached maximum size. When Principal Applecrab, patted Theo on the shoulder, Baby Theo got jealous and went into a rage fit, causing panic and destroying everything in the school. Theo claimed that he learned the violent character traits from Gwyn's aggresive energy, being inflicted upon him, throughout his life.
Luc eventually came in, summoning his own mutation, Giant Maggot as an opponent to take down Baby Theo. However, his facts on fauna were wrong, as he thought worms ate birds. Baby Theo easily knocked out the Giant Maggot, forcing him to fart his cocoon fabric all over himself. He then went through an extremely quick metamorphasis and came out as a giant butterfly, which became the best of friends with Baby Theo and they both flew off together, until Luc dwelt upon the fact that chickens couldn't fly, dropping Baby Theo out of flight.