When the parents are in the toy car riding on the track there is a scene where a bulldozer is about to wipe them out but in several shots the car has yet to cross in front of the bulldozer yet between those scenes the car has already passed the dozer.
When Mitch discovers Diane and Patty on the table, there is a shot where he bends down and says "Mom?" In this shot, Patty is on the left, and Diane is on the right. It cuts to both of them nodding, and they have switched sides. Then it cuts to Mitch fainting, and they are back in their original positions.
Wayne suggests drinking milk to disperse the glowing liquid throughout the body by using the "calcium channel". Calcium channels are found in muscles and bones and help regulate muscle and nerve function. It's not a transport function.
When the Szalinski brothers are fighting after being shrunk, they turn around to see Diane walk in the attic. As they turn around, you can see their shirts cut off from the green screen chroma key effect at the right of the screen.