Kimmy was a modern "Added so we can have more girls, but we actually made her a fun character.. thing is, this isn't a show about having good/fun characters, it's a show about fucked up, flawed people" character
Suzie was just a competent neighbor character. I liked how she felt the most like a real little kid, precocious and smart but still with emotional vulnerability here and there. Exactly what a 3 year old with a hyperintelligent 5 year old brother, competent teen sister, and rich parents is like.
i dont know the oddparents ones because i stopped watching that show by that point, which is the definition of a poochie. people stop watching, so they start adding more new characters to try to get people back. I've never SEEN anything from the first two, but the last one got BlueJr to draw more fanart, so I am pretty sure that one WORKED. it got people to go watch, to see what she was like.