Factual error: In the beginning sequence where they show the sperm first fertilizing the egg, it is biologically incorrect - only the head part of the sperm enters an egg, everything else stays on the outside and eventually dies off.
Revealing mistake: When Molly's mother is listening (to what she thinks is sex) outside the apartment door, the handle is shown on the right side of the door. But anytime after that the door opens from the left side. Both doors open on the left. (For some reason Molly has 2 front doors to her apartment).
Continuity mistake: When Molly takes Mikey to the Chubby Charles office to meet Albert, she changes his poopy diaper and slams it down on his new desk, rendering it junk. She then puts Mikey back on the floor, but never snaps the legs on his overalls. In the next shot, you see Mikey smashing Skeletor on the floor and his snaps are done, but when Molly picks him up to leave the office, they are undone again.
Continuity mistake: There is a car chase scene where they show him driving wearing sunglasses, then they cut back to him and he's not wearing them, then they cut back to him and he is wearing them...
Continuity mistake: After Mollie was called by the elderly housing unit's administration, in the scene that she is cleaning up Grandpa's mouth, she is using a piece of a cotton roll and its package, which is cylindrical, is on the table. After a few shots, Mollie is still cleaning up Grandpa's mouth, but with a tissue, and the tissue's package, which is rectangular, is on the table too.
Continuity mistake: While Mollie is hitting James with the broom, a box of Cheerios falls off the shelf and gets wedged between the shelf and wall. Soon after they sit down the box of Cheerios is not there anymore, nor is it on the floor. Also, a white knick-knack on the shelf is now on its side and books that were not there before have appeared.