Charlie is the second son born to Molly and Arthur Weasley of the Burrow in Devon.
The year of Charlie's birth is determined from Rowling's statement on her website that Bill is two years older than Charlie, who is three years older than Percy and also from various canon passages which describe Charlie's Quidditch career at Hogwarts. The actual month and day are also Jo's original website (JKR).
Rowling's statements about the ages of the two oldest Weasley boys seem to be inconsistent. However, careful analysis of all canon facts shows it to be all but certain that Charlie left Hogwarts in his sixth year to go study dragons in Romania. The Lexicon uses this logic to determine the dates for Bill and Charlie's timelines because it is the only way to satisfy all canon references.