סימן קכא סעיף ט
עוֹד יֵשׁ קֻלָּא בְּג' הַתַּעֲנִיוֹת הָרִאשׁוֹנוֹת, דְּעֻבָּרוֹת וּמֵנִיקוֹת הַמִּצְטַעֲרוֹת, פְּטוּרוֹת מִלְּהִתְעַנּוֹת. וְכֵן חוֹלֶה, אַף עַל פִּי שֶׁאֵין בּוֹ סַכָּנָה, לֹא יִתְעַנֶּה. וּמִכָּל מָקוֹם אַף מִי שֶׁמֻּתָּר לוֹ לֶאֱכֹל, לֹא יִתְעַנֵּג אֶת עַצְמוֹ, אֶלָּא יֹאכַל מַה שֶּׁהוּא צָרִיךְ לִבְרִיאוּת גּוּפוֹ (תק"נ תקנ"ד). וְכֵן הַקְּטַנִּים, אַף עַל פִּי שֶׁאֵינָם חַיָּבִים לְהִתְעַנּוֹת, מִכָּל מָקוֹם אִם יֵשׁ בָּהֶם דַּעַת לְהִתְאַבֵּל, רָאוּי לְחַנְּכָם, שֶׁלֹּא לְהַאֲכִילָם רַק לֶחֶם וּמַיִם, לְהִתְאַבֵּל עִם הַצִּבּוּר.
There is still another lenient feature regarding the first three fasts: pregnant and nursing women, are exempt from fasting, if it causes them discomfort.2They are permitted to eat, even if they have no discomfort; except that our women have elected to be stringent and eat only if they experience discomfort. If they are weak, however, they should not practice this stringency, and they should not fast. (Mishnah Berurah 550:5) Also, a sick person, even if he is not critically ill, should not fast.3It is forbidden to practice stringencies in this situation. (Ibid 550:4) Nevertheless, even a person who is permitted to eat, should not enjoy an elaborate meal, but should eat only as much as he needs to preserve his health. Children, too, although they do not have to fast, nevertheless, if they understand the significance of mourning, it is proper to train them, and give them only bread and water,4They may be given any other simple food. (Ibid. 550:5) so that they will be part of the communal mourning.
תנא דבי אליהו כל השונה הלכות בכל יום מובטח לו שהוא בן העולם הבא שנאמר הליכות עולם לו אל תקרי הליכות אלא הלכות (נדה ע"ג.)