Baby Thaddeus only appears in the episode "Dirty Rotten Diapers". Despite his name and appearance, he was actually an adult gangster diagnosed with dwarfism who used his small size and child-like appearance to commit crimes. His main scheme involved having his two henchwomen, Pomona and Monrovia, run a fake adoption agency. Unsuspecting couples would adopt what they thought was an orphaned baby and take him home. During the night, Thaddeus' henchwomen would come and rob the place, forcing the couples to give up their "baby", not realizing that he was actually behind the robberies.
Becoming bored of their adoption racket, Thaddeus has his minions place him on the doorstep of a wealthy childless couple. It was during this time that the Rescue Rangers began investigating the robberies. Suspecting Thaddeus, Chip and Dale were able to get inside the house by fooling the couple into taking them in as pets. The rangers' initial attempts to bring Thaddeus to justice were hampered by Thaddeus as well as Gadget's recent desire to be nonviolent when solving crime. Eventually becoming angered, Gadget would set aside this desire and attempt to stop Thaddeus at any cost. Luckily, Thaddeus would be stopped before he and his minions could rob the wealthy couple, and were arrested by police, who became aware of Thaddeus' true nature as an adult, if pint-sized, crook.
Esther from the horror movie Orphan is similar to him in that she is an adult criminal with a form of dwarfism that makes her appear childlike. However, Esther is a serial killer and arsonist rather than a robber.