WHenITS THEIR BIRTHDAY,AND WHAT YEAR WHEN THEIR BORN?

Butters: Sept. 11th
Kenny: March 22nd
Cartman: July 1st
Stan: October 19th (Trey Parker's Birthday)
Kyle: May 26th (Matt Stone's Birthday)

Unsure about Wendy and Craig. And on "You Have 0 Friends" it showed on their Facebook pages that they were born in 2001.

Sources: South Parkism's website; they are holidays of the church, Butters' birthday is revealed in "AWESOM-O".