In the cab, on the way to the hospital, Mollie shouts that her water just broke and James looks back apparently seeing a mess, but when she gets to the hospital, her overalls are perfectly dry with no evidence of her water breaking.
Mollie's blind date stresses the importance of a Notre Dame football game on TV by saying "it's the playoffs." In 1989, Notre Dame participated in Division I (now the FBS), which had not yet incorporated a playoff system.
At one point, Molly is in the streets with Mikey and we see a Starbucks Coffee in the background. Starbucks did not make it to the east coast until the early-1990s.
When James is driving Molly to the hospital, they pass a window and you can very obviously see the camera sitting on the hood of the taxi.
When Molly and James are in the airplane and he's telling her to "take his stick", you can see the wall of the hangar behind them during the front shot.
In the far shots during the chase scene at the end it is obvious that the driver and passenger in the taxi are Travolta and Alley's stunt doubles.
When James goes to Mollie's apartment to return her purse after Mikey is born, James says to Mikey, "How you doing, Mikey? I'm James." How did he know his name was Mikey if Mollie never told him?
James introduces himself to Mikey and he shakes his hand with his right hand. In the next shot James is shaking Mikey's hand with his left hand.
James carries a sleeping Molly to bed. When he first picks her up, her hands fall on her chest. However, in the next shot, her arms are wrapped around his neck.
When Molly is dressing Mikey for his first meeting with Albert, she asks him what outfit he wants to wear. In the shot with him saying neither, he is already in the white lamb overalls.
When the channels are being switch by a remote control from a football game to a snuggle's commercial, the channel number stays at 03.
When James is driving Molly and Mikey to pick up his grandpa, they pass several windows that reflect the camera and crew on the other side of the taxi.
During the very last scene James and Mikey go to a hospital to see Molly. While walking into her hospital room you can see it's obviously a set/sound stage when you look up at the top, in the corner(s), you will see it for a few good seconds.
When Molly is in the hospital talking to her baby through the glass about finding a father, she is only wearing 1 earring.
James' sunglasses while driving around looking for the missing child.
In every shot of Mikey in his high chair except the very last one (the dance sequence), the background dishes in the drainer with the towel tossed over the counter can be seen to be exactly the same.
During the chase scene at the end of the film the windows in the taxi are down during close-up shots and up during long shots.
The mess made during fight between Albert and James is different in every shot.
When Mikey hops in the car being towed and thinks he's driving, the front door was still open, but when the car is seen being towed away, the door is closed.
When Molly is cleaning excess chocolate off Grandpa's face, the box of tissues keeps changing.
After the fight with Albert, the red table that the phone was on had nothing on it. When Molly came home, the section of the room was trashed in a complete different way with trash on the red table.
When James and Albert fight, the flower falls from the table twice.
When Molly starts hitting James for taking Mickey out without permission, he falls knocking a box of Cheerios which hangs curiously over the counter and has a plastic glass standing upright untouched. After he has removed the splinter, we see the box gone and it is replaced by the same plastic glass fallen down and it's contents spilled over.
James attempts to light a cigarette in Molly's apartment to her disgust. However there is a sign displayed in his cab that states the driver is allergic to cigarette smoke.
After Mikey finishes making the statues fight, the small statue on the back is leaning one way, then in another shot it's leaning the other way.
When Mikey is making the statues fight, a ball breaks off of one of them and rolls on the shelf. When Molly fussed at him and he asks "What did I do?" the ball is gone.