Experiment - S5-E18
Revealing mistake: In the first scene, Lois is feeding Jamie while talking to Dewey. In the next clip, it changes to just a prop baby doll toy with a beanie covering a majority of his face. (00:04:25)
Revealing mistake: In an imagination sequence Reese and Malcolm are throwing around Jamie, but you can see it is a doll.
Revealing mistake: When Lois confronts Susan about not telling her about Susan's kidney disease, Susan is telling Jamie how cute he looks in his sailor outfit. When the camera is moved to a different angle, it becomes very obvious that "Jamie" is just a prop baby doll. (00:11:10)
Revealing mistake: At the end, Malcolm speaks to camera with several children moving in the background. One boy doesn't know where or when to move and he tries to speak to someone off camera. In the end he gives up, shrugs his shoulders and walks off.
Revealing mistake: When Kristen starts taking her helmet off you can see her hair is actually a wig.
Answer: It is made up - although it is implied she is Croatian, she never mentions it herself.