Question: I've never adopted kids before so that's why I'm asking this question; When Stuart is being adopted, I noticed that on his papers, the parents were listed as Mr. And Mrs. Little. My question is, why aren't their first names on there? George's first name was, so why weren't theirs on there as well? Is that a mistake or is it common?
Question: How come the humans can understand mice and birds, but not cats?
Answer: Since there no scenes of cats trying to communicate with humans, we don't actually know if humans can understand them or not. It may be that cats can communicate with humans, but simply choose not to.
Answer: Because it's a movie when talking animals is possible but not all animals can talk to humans.
Question: What was the point of George's lucky underwear line? (00:34:45)
Answer: It was just an excuse because George didn't want to be in the race anymore after the remote control got broken.
Well, it was an accident with Stuart throwing the remote control for the boat, and was broken and stepped on by the man's foot.
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.