As is true regarding all other mitzvot, we are commanded to educate our children to keep the mitzvot relating to Tish’a B’Av and mourning over the churban. Since children are weak, however, it is impossible to teach them to fast [when they are young]. Therefore, we train them to fast a few hours, depending on their strength, only starting from age nine. They should not fast the entire day (Rama of Panow 111; see K.H.C. 554:23). When feeding children [on Tish’a B’Av], one should give them only simple foods, in order to teach them to join with the community in mourning (M.B. 550:5). Many people are careful to teach their children who have reached the age of chinuch (education) – from around six years old – not to eat or drink on the night of the fast.
At the age of chinuch… when a child begins to understand the story of the destruction and the [concept of] mourning over it, we teach him or her not to wear leather sandals or shoes and not to apply ointments or bathe for the sake of pleasure. Some act strictly in this regard even from the age of two or three. Even though children of this age do not understand the concept of mourning, [these acts nonetheless symbolize] a sharing in [the Jewish people’s] anguish and demonstrate our grief over the churban, seeing that even small children participate, in some way, in our mourning.
[As mentioned] above (10.10), one is forbidden to study Torah [on Tish’a B’Av], because it brings a person joy, and one may only learn sad topics related to the destruction of the Temple and the laws of mourning. The same applies to teaching children: adults may only teach them topics related to the churban and mourning. Some say that adults may not teach children even those topics and laws related to the churban, because adults feel joy when they teach children. [According to these authorities], the only thing one may do is tell them the story of the destruction (M.B. 554:2; see K.H.C. 8). Since these two opinions are equally [represented], every person may choose which one he wants to follow. Everyone agrees, however, that a minor may learn, on his own, whatever an adult may learn.
. Actually, with regard to Yom Kippur, the Shulchan Aruch (616:1) rules that children must observe only the prohibition against wearing shoes – because doing so does not cause that much pain – while washing and anointing are permitted. Nonetheless, the reason for this leniency is that people used to wash and anoint young children in order to foster growth. Today, however, when we do not follow such a practice, it seems that washing and anointing are forbidden just like wearing shoes is. Nit’ei Gavri’el 69:2, 73:3 advances this logic. The Chochmat Adam (152:17) writes that one need not train children [on Tish’a B’Av], even with relation to wearing shoes, because we educate children [to observe these laws] only on Yom Kippur, but onTish’a B’Av and in cases of personal mourning, there is no need to do so, if it entails even a small degree of pain. The Magen Avraham (551:38), however, asserts that we educate children [to keep the laws of] public mourning. The Mishnah Berurah (551:81) concurs, adding that there are two reasons why [adults] may not give haircuts [to children during the Nine Days]: 1) for educational purposes – accordingly, the prohibition starts at age six; and 2) to generate feelings of sorrow among the adults – in which case the prohibition starts even before then. The author of Piskei Teshuvot (554:15) concludes that, either way, everyone agrees that there is no need to be strict before the age of two or three.
. The Bach, Taz, and others [assert] that children who understand what they learn may study sorrowful topics, and when [our Sages] say that it is forbidden to teach children, they mean [it is forbidden to teach them] their regular course of study. The Magen Avraham maintains that [an adult] should not teach them even sad topics, but one may tell them stories about the churban. See R. Karp’s [Hilchot Chag BeChag] 7:42 and Torat HaMo’adim 8:20.