All must fast, including Baalei Habrit (i.e. the Mohel, the Sandak, and the father of the baby). Pregnant and nursing mothers are required to fast.
Fasting is the most important aspect of Yom Kippur and takes precedence over going to Shul and reciting all the Tefillot. One who might not be able to complete the fast if they go to Shul should stay at home. [If necessary, a husband should facilitate his wife's fasting by going home during the break to help out with the children. If necessary, he should do so even during davening, or arrange help.]
The ill/elderly, a woman who recently gave birth, or a pregnant or nursing woman who feels excessive weakness, should consult a Rav. A Rav should also be consulted regarding medicines.
One exempt from fasting does not make Kiddush or eat Lechem Mishneh. [It is best to avoid bread, as there are many particulars regarding washing for bread and Birchat Hamazon on Yom Kippur.]
One may touch food, but may not engage in its preparation, lest he forgets and eats it. Therefore, one should not prepare food for children and those exempt from fasting, unless they cannot do so themselves. One who normally washes his hands before handling food may do so on Yom Kippur.
When a Brit occurs on Yom Kippur, the Seudah takes place at night, after the fast. [The actual Brit takes place before Musaf. Since no one can drink the wine, a drop is given to the baby who is having the Brit.]
