Continuity mistake: None of the Sheffield children are aged properly over the course of the series. It's established that Grace is 6 years old in season 1, but two years later in season 3 she's 10. Maggie is 18 at the end of season 5 but turns 21 years old in early season 6. And finally, Brighton is in seventh grade in season 2 and somehow is graduating high school at the end of season 6 (when he should be only a junior, and nothing about Brighton's character would suggest he's capable of skipping a grade).
Continuity mistake: In the opening sequence, Fran arrives at the Scheffield house with a case of make-up. When we see a shot of the makeup head on, one can see two lipsticks at the far left corner of the case. When we see a shot of the case from behind, the lipstick is now at the right corner of the case.
Continuity mistake: In the dining room, CC is wearing a scarf over her head as part of her "safari" outfit. When the shot shifts to a close-up of her looking horrified at the thought of taking the kids to the Zoo on her own, the scarf is suddenly around her neck.
Continuity mistake: In the kitchen at the beginning, Fran pours milk into three glasses. After she fills the third glass, she starts to put the milk down. In the next shot, she is holding the bottle up to the glass again and pours some more milk before putting the bottle down.