Darcy Rose Byrnes joined Desperate Housewives in its seventh season, replacing Kendall Applegate as Penny Scavo.
No reason has been provided but it is most likely that the show needed an actor that will be approapriate to the age being portrayed by the character. As the show progresses, viewers need to see a growing Penny as well.
It is not the first the show has done such character replacement.
Penny Scavo, the eldest daughter of Tom and Lynette Scavo in has been portrayed by several child actors.
Twin brothers Dylan and Jordan Cline were the original portrayers in season 1; Darien Pinkerton and Kerstin Pinkerton, identical twin sisters, acted Penny Scavo in seasons 2-4. Applegate and Byrnes appeared in seasons 5 & 6 and 7 & 8 respectively.
From 2004 until 2012, Desperate Housewives ruled Sunday nights. Ever wonder what all the Wisteria Lane kids have been up to since the comedy-drama went off the air a few years ago?
See this gallery (via WomansWorld.com) to see the housewives' children then and now.