Visible crew/equipment: When Carrie notices that Doug has walked out the room, there are some tape markers on the floor from where Doug was stood. (00:09:40)
Continuity mistake: When Carrie say to Doug that they are sleeping on the fold out couch, her arm goes from on her hip to hanging by her side instantly. (00:11:00)
Continuity mistake: Carrie cuts Kirby's burger in half with a knife in her right hand. Camera cuts and a fork has appeared in her left hand. (00:10:30)
Continuity mistake: When Carrie is serving up the burgers for dinner, she places one on Kirby's plate. Camera cuts to Kirby sitting down and the burger has vanished. (00:10:25)
Continuity mistake: When Carrie suggests about them looking after the kids to Doug, he has his arm up by his chest. When the camera changes it's lowered. (00:04:20)
Continuity mistake: When Doug and Carrie are in Deacon's kids' room, Carrie is changing the baby and between shots the baby changes from lying down to sitting up. (00:15:00)
Answer: Sara hasn't been mentioned in later episodes, and it suggested in later episodes that she never existed, and that Carrie is an only child. Kevin James stated that the producers couldn't think of an good plots to use with Sara, so they left her out.