This is a tradition based on the Biblical blessings our patriarch Isaac bestowed on his sons, Jacob and Esau, and our forefather Jacob tendered to his grandchildren , Ephraim and Menasseh. Yesimkha Elohim k Efrayim v k Menasseh. May God make you like Ephraim and Menasseh. May God make you like Sarah, Rebecca, Rachel and Leah. In most families, the kiddush is recited by one person, while the rest of the family stands.
Standing allows everyone to attend to the sacredness of the moment.
While kiddush is recited, the challot are covered so as not to detract attention from kiddush. The Heavens and the earth and all that was in them were completed. And God completed on the seventh day all the work that he had done. And God rested on the seventh day from all the work that God had done. And God blessed the seventh day and sanctified it , for on that day God rested from all his work, which God had created.