During the entire Three Weeks, certain activities are abstained by Jews observing Jewish law in order to commemorate, remember and inspire mourning over destruction of the Temple.
"[1] The Nine Days inaugurates an even greater level of communal and personal mourning in recognition of the many tragedies and calamities that befell the Jewish people at this time.
[2] Rather than view the Three Weeks and the Nine Days as times of punishment and self-mortification, some Jewish teachings see them as opportunities for introspection, repentance, and forging a closer relationship with God.
The custom is also to avoid saying the blessing over a new fruit on a weekday (one may do so on Shabbat), and making a major purchase such as a new home or car.
[8][9] Children, pregnant or nursing women, and old or sick people who must eat meat for health reasons are allowed to do so.
[10] Children under the age of Bar and Bat Mitzvah are generally included in the lighter mourning practices as training for mitzvah-observance.
While swimming and water sports are avoided, camps often run special study programs and Holocaust education modules.
[11] On Tisha B'Av itself, campers gather to listen to the traditional reading of the Book of Lamentations and engage in creative projects that express the themes of the day.
Therefore, observant Jews eat meat at their Shabbat meals and drink wine or grape juice for Kiddush as usual.
[2] Throughout the Nine Days (excluding Tisha B'Av), guests at a seudat mitzvah—for example, a brit milah ceremony, a pidyon haben, a bar mitzvah seudah on the boy's birthday, or a siyum—are allowed to eat meat and drink wine.
[2] Some yeshivas, kollels, and other study programs try to plan the completion of a volume of Talmud or Mishnah to coincide with the Nine Days so that a meat meal may be served.
The Sages enforced this extension of the mourning period to reflect the fact that while the Temple was set on fire during the afternoon of Tisha B'Av, it continued to burn through the Tenth of Av.