Everyone needs a day of rest.
Jewish answer:
Because God commanded it. Its origin is in the Torah (Genesis ch.2, Leviticus ch.23, Exodus ch.20 and many other passages).
The Jewish Sabbath is from Friday sundown until Saturday after twilight. The Sabbath is a day blessed by God (Genesis ch.2), a day of rest (Exodus ch.20, ch.31), and a day of strengthening ties with the family, the community, and with God.
They prepare their children for Shabbat and light the Shabbat candles.
"Shabbat Shalom!"
They're called Shabbat candles (Neirot Shabbat in Hebrew).
Shabbat Shabbatot
After Shabbat, there is the Havdalah service.
Shabbat comes from the Hebrew word for sit/rest. Shabbat is the day of rest.
Shabbat shalom is a Jewish greeting which we say during the day of Shabbat. See also:More about the Jewish Shabbat
Shabbat Shalom (שבת שלום).Note: This means 'A peaceful shabbat'. The phrase "happy shabbat" is not a phrase that is traditionally used.
There is no issue with swimming during Shabbat, however, you wouldn't be able to shower after swimming until Shabbat ends. (Assuming you wish to be Shabbat observant.)
Judaism.See also:More about Shabbat
There is no reason to not allow Shabbat.
They say Shabbat blessings for their children.