Continuity mistake: Hal speaks about having held Malcolm the moment he was born. But in the Season 2 episode "Flashback" not only was he not there for his birth, he didn't hold him immediately, instead he talked to Lois.
Continuity mistake: During the scene when Lois says that Malcolm is a genius, his arms keep changing position between shots.
Continuity mistake: Halfway through the episode, the bedroom door is open in the wide shot. In the over-the-shoulder and closeup shots, the door is closed. (00:10:09)
Pearl Harbor - S6-E4
Continuity mistake: Reese had a lot of food in his bowl (when complaining about the low-fat food she has made them eat), then Lois puts food in his suddenly empty bowl. (00:05:25)
Continuity mistake: When Lois goes outside to meet Hal at the clothesline, she leaves the door open. In a few shots during their conversation, the door is closed in the background. (00:06:20)
Continuity mistake: When Malcolm goes into the classroom and gives his teacher a hamburger she eats about half of the burger really quickly but in the next shot of the hamburger there appear to be only a few bites taken.
Living Will - S6-E12
Continuity mistake: In Season 2: Episode 15, when Francis and a group of people are volunteering at the Lucky Aid, Craig mentions to them that he might've accidentally mailed the marked inventory numbers to his mother. However, in this episode, Craig has never seen or interacted with his mother because his father told him when he was a child that she passed away.
Continuity mistake: When Lois fights with the woman in the mud puddle, the tug of war rope is seen dropped on the ground, and then tense again. This alternates between close and far shots.
Halloween Approximately - S2-E2
Continuity mistake: When Francis walks into the boy's room the calendar says September 2000. In the next shot it changes to October 2000. After that Reece says "No, it really is the 31st" he flips up the September page of the calendar to October. (00:06:15 - 00:07:15)
Continuity mistake: In the bowling alley, the design above the pins is blue and pink pins. While in the back of the bowling alley, above the pins is a different design.
Continuity mistake: In the side of the story when Lois takes the boys, Malcolm has some kiddy bumpers put in to help him bowl. In the next scene when Reese is about to tell Beth the joke, you can see the lane which Malcolm was just at but there are no bumpers in the gutters. Then later when Malcolm stands up to Lois they are back in the gutters.
Answer: It is made up - although it is implied she is Croatian, she never mentions it herself.