Eating restrictions for one who is exempt from fasting:
Eating in accordance to “Shiurim” as required on Yom Kippur: Some Poskim rule that even one who is exempt from the fast is required to follow the same eating and drinking measurements “Shiurim” prescribed on Yom Kippur. Other Poskim, however, rule it is not necessary. Practically, the custom is not to follow this opinion, and hence one who is permitted to eat or drink may do so without limitation.
The menu-what may one eat and what to avoid: If one is not fasting that day, such as a pregnant or nursing woman, it is proper to diminish somewhat in eating and drinking in order to participate in the day of oppression followed by the community. Accordingly, they are to avoid eating meat and drinking wine, unless they are weak and need it for their strength. Some Poskim rule that a child who has reached the age of understanding the mourning is only to be allowed to eat bread and water or other simple staple food. The custom however is not like this opinion. [However, they are not to be given sweets and the like, although one is not required to stop them from eating it if they are in the midst of doing so. The same applies to an adult who is exempt from the fast, that he should not eat candies and treats, and avoid the eating of delicacies.]
May one who is not required to fast eat in public? If the reason for their exemption is not readily apparent, they are not to eat or drink in public.
Should one who is exempt from fasting redeem the fast with a donation towards charity? It is proper to do so.
Must one who is exempt from fasting try to fast for a few hours in the morning prior to breaking their fast? No. They may eat immediately in the morning.
 Tzemach Tzedek O.C. 108:110; Divrei Nechemia 42; Sefer Haminhagim p. 92 [English] regarding all four fasts and in footnote 342 even regarding Taanis Esther; Halachos Ketanos 2:100; Mahrahm Shick 289; Shaiy Lamorah 4; Marcheshes 1:14; Biur Halacha 554 “Bemakom” in name of Pischeiy Olam
 Chida in Machazik Bracha, brought in Kaf Hachaim 554:31; Mahraham Shick 290; Avnei Nezer 540; Aruch Hashulchan 554:7
 Shevet Halevi 4:56; Kinyan Torah 1:118; Tzitz Eliezer 10:25-16; Shraga Hameir 1:59; Piskeiy Teshuvos 554:9; Hiskashrus 889 that so he received from several Rabbanei Anash, despite the ruling in Sefer Haminhagim ibid; Some suggest the entire reason behind the Shiurim recorded in the previous Poskim who are stringent is order to also gain the advantage of being considered to have fasted, and hence be able to count for a Minyan for Kerias Hatorah, and saying Aneinu and the like, however not that one is required to follow these Shiurim. [See Hiskashrus ibid; Piskeiy Teshuvos ibid and 566:6; Marcheshes ibid]
 Michaber 554:5 regarding pregnant and nursing women; Ashel Avraham 686 Mahadurah Tinyana; Chayeh Adam 133:6; M”B 550:5; Kaf Hachaim 550:7
 M”B 550:5; See Seder Hayom Inyanei Bein Hametzarim; Piskeiy Teshuvos 5508
 M”A 550:2; Rameh 111; P”M 549 A”A 7; Chayeh Adam ibid; M”B ibid; brought in Kaf Hachaim 549:8 and 550:9
 Some write this is starting from age nine. [See Piskeiy Teshuvos 550 footnote 11]
 Birkeiy Yosef 549:1; Daas Torah; Kaf Hachaim 549:8 and 550:9; Beir Moshe 8:95
 Beir Moshe ibid; Piskeiy Teshuvos 550:3
 Shaareiy Efraim 1:10; Minchas Elazar 3:3 based on Eiruvin 41a; Teshuvos Vehanhagos 2:265; Piskeiy Teshuvos 550:2
 Mateh Efraim 602:23
 Avnei Nezer 540; Orchos Chaim 550:3 in name of Shut Ramatz; See Piskeiy Teshuvos 550:1-2 and footnote 2