Before the intro credits, while the Formans are eating breakfast, Red is holding a bottle of maple syrup. When he offers to find Kitty a cheap contractor, the yellow bottle cap is off the bottle. Moments later, when the shot cuts back to him, the lid is on the bottle.
The font on Eric's Spider-Man pillow case wasn't introduced until the '90s.
At 16:40, when Theo & Leo bring the Formans down to see the basement, a clap board is seen on top of the television set. Later, at 18:50 (in the same scene), it is gone.