Revealing mistake: Throughout the entire series there is one staircase upstairs and two downstairs. And, they more than likely are not the same staircase because the two downstairs are on opposite ends of the house.
Factual error: In the episode entitled 'Paper or Plastic' where Lucy gives birth, she gives birth in the elevator and when the doors open she is standing there holding her daughter. I can excuse the standing minutes after giving birth, but she is still fully clothed. The paramedics would have removed her skirt and underclothes so as not to ruin them (giving birth is messy) and they would not have redressed her. She is then shown laying on the gurney fully clothed, no blanket covering her.
Continuity mistake: In the Valentines Day episode when the whole family is waiting to be seated for dinner, they show a shot of Kevin holding baby Savannah, she is asleep against his shoulder. They switch to a shot of Simon and Rose saying hello and switch right back to Kevin and baby Savannah, who is now wide awake sitting up in his arms.
Continuity mistake: In the episode titled "And Baby Makes Three" After giving birth Sandy is laying in the bed talking to Martin holding the baby. Her hands alternate between shots of cradling the real baby on face shots to lying in her lap, while a "doll" lies in her arms in the shots over her shoulder.
Factual error: In the episode entitled PAPER OR PLASTIC where Lucy gives birth, she is stuck in the lift in labour. Lucy is lying on a full size mattress. The paramedics could not possibly have passed something that large down the liftshaft and into the relatively small hole in the roof of the lift.