George Little: Maybe we should go home.
Mr. Little: Why?
George Little: I'm not wearing my lucky underwear.
Mr. Little: You don't have lucky underwear.
George Little: Well, maybe we should get some, and then come back for another race.
Snowbell: I can't believe I'm arguing with lunch.
Snowbell: Didn't your mother warn you that you shouldn't go out into Central Park at night?
Smokey: My mother was the reason you shouldn't go out into Central Park at night.
Stuart Little: Snow, where are you going?
Snowbell: Oh, I gotta yawn, stare at traffic, lick myself. And believe me, that could take hours if you do it right.
Snowbell: You think you could help me?
Smokey: Consider it done.
Snowbell: Thank-you Mister Smokey sir, how could I ever think you?
Smokey: Don't worry Tinkerbell, anytime.
Snowbell: Tinkerbell! Ha Ha, He called me Tinkerbell! You're a funny guy.
Smokey: Yeah, whatever. house cats, Sheesh.
Snowbell: I lied, okay? Welcome to Manhattan.
Mrs. Little: Is he going to be all right?
Dr. Beechwood: Well, a lad that size swallowing all that detergent. Amazingly, I think he's gonna be fine. Also, he's very clean.
Mrs. Little: He hates us.
Mr. Little: We've never been hated before.
Anton, the stuck-up bully: Gee George, you all done crying?
George Little: Yeah! Are you all done being a jerk?
Anton, the stuck-up bully: No.
Stuart Little: So, what do I call you?
Mrs. Little: Mom.
Mr. Little: And Dad.
Mrs. Little: We haven't told you the best news of all.
Mr. Little: You have a brother, named George.
Stuart Little: What do I call him?
Mrs. Little: George.
Race Spectator: Who is that mouse anyway?
George Little: That's no mouse, that's my brother.
Answer: I wouldn't call it a "mistake" as the movie did that on purpose for both a gag and an emphasis on Stuart becoming a Little. This is definitely not practice for actually adopting children. You must put your first name on the paperwork.