When Lois wanted to check her pregnancy test, she had to go to the bushes to do it because the bathroom was occupied. But in a previous episode it was revealed that the family has a 2nd bathroom which they thought was a closet.
Lois gave birth to Francis on their wedding day, meaning his birthday is on their wedding anniversary. These two celebrations never cross over in subsequent episodes.
On the scene that Louis sits to give birth to Dewey, Hal's hair changes from wet to dry and back several times.
When Dewey is talking to Malcolm, Dewey's stuffed toy changes position on the pile of magazines.
Lois is pregnant with Dewey. A cop delivers Francis to the front door. Sometimes he has a hand on Francis's shoulder (or not) depending on camera.
During the cold open, just after the ball is thrown into the sewer, a lighting rig can be viewed quite clearly to the left of the screen.
At the start when the boys are throwing the baseball trying to keep it away from Dewey, a camera and lights can be seen to the left of the screen.
When Hal gets out of his car in the flashback, the shadow of the camera is visible.
In the beginning of the wedding scene, the camera can be seen in the left side of the screen.
In the flashback when she goes into labor with malcom the camera and cameraperson are reflected in the back window of the car.
In the flashback prior to Malcolm's birth, toddler Reese is 2 years old and has blue eyes. But Reese is supposed to be a little more than 1 year old than Malcolm and has brown eyes.