Continuity mistake: In "Our Son, the Man", Greg wants his own room. One night, while in bed, Mike and Carol discuss their options. Carol says, "How about the attic?" Mike responds with, "That would be fine if Greg were only two and a half feet tall." Later, they give Greg the den for a while. However, in "A Room At the Top", after cleaning out the attic, which was now full size, both Greg and Marcia want it for their own private room.
Other mistake: A final contest is given for control of "green stamps" with all the kids building a "House of Cards." Whomever causes the cards to fall will be the losers. All is going well until Tiger comes in and knocks into Greg and causes him to bump the table and knock over the cards. If you watch closely at the end of the scene, when all the dialog is finished, you can see Mike trying to knock down a few remaining cards. However they keep popping up. Probably due to the fact that the cards were glued together to make it easier for the kids to build upon.
Continuity mistake: When the vase gets broken, it's easy to see that one large piece flies off the chest of drawers onto the floor. And when the boys look down at the broken vase from upstairs, three pieces are on top of the chest of drawers. But Greg - seen later trying to fix it - says something to the effect of "Good thing it only broke into three pieces." So what about the piece that flew off onto the floor?
Continuity mistake: When the kids are building the card castle to see who would get to choose what they get with the stamps, Jan is putting a card on, in one shot her hair is up in a ponytail then in the other shot her hair is down. This happens back and forth when the shots change.
Continuity mistake: Near the beginning, Greg is painting the shutter green, he gets a phone call and goes inside. The paint bucket falls on Bobby because the ladder falls. Greg sticks his head out the window and asks who took his ladder. The shutter now has no paint on it.
Deliberate mistake: When Bobby's at the treehouse the second time for his initiation into the club, there's a boy already up in the treehouse, and after Peter takes the birdcage from Bobby's hand, the next closeup of the boy in the treehouse is a flipped shot, note the wood boards.
Audio problem: When the kids are painting a cardboard tree for the play, they ask their dad what he thinks of it. He then says "you better ask the two poodles next door." As he walks away he seems to almost trip/fall over something. Then the mom is heard laughing, even though she's not in the scene.
Continuity mistake: When Cindy goes downstairs to ask "isn't anyone coming up to say goodnight?" or something similar, when Alice is talking to Mike and Carol about Sam not coming over, Cindy is wearing her pyjamas. She then gets in trouble and goes straight back up to her room and she is suddenly dressed in jeans and a top - her hair has different hair ties in it too.
Continuity mistake: When Marcia takes her last turn placing a card at the top of the tall house of cards, in the shots facing her she's stressed about accidentally collapsing the cards so she holds back her charm bracelet with her left hand, but in the first shot facing the three boys Marcia's left arm is down at her side and the charm bracelet is dangling at her wrist, right beside the cards.