In which direction is Kaddish recited and can a child be part of a Minyan?
Although the practice is to face towards the Bet HaMikdash-in most cases, east-when praying, there does not appear to be a hard and fast rule with regards to the recital of Kaddish. Rabbi David Ovadia (Nahagu Ha’am, Hilchot Kaddish) writes that in Morocco, the custom was that Kaddish did not necessarily have to be recited facing east. This is relevant when Kaddish is recited around a table during a meal and the like, and the custom is to not be particular about finding which way is east. Evidently, if one is in the sanctuary of a synagogue, it is not proper to have one’s back towards the Hechal, but otherwise there is more leeway.
The Shulhan Aruch (O.H. 55:1), when discussing the laws of Kaddish, says that Kaddish, just like other holy acts (reciting “Barechu”, Kedusha, etc.) must be recited in the presence of ten adult men. It goes on (ibid:4) to reject the opinion of the Tosafot, who say that when a congregation is hard-pressed to find a tenth man, a minor as young as six years old who knows to Whom one is praying may be counted as the tenth person. The Tosafot say that in such a situation, the minor should hold a Humash in his hands, since its holiness elevates the status of the minor. The Rama (ibid.) writes that even while holding a Humash, a minor should not be counted as part of a Minyan, but that there are lenient opinions in urgent situations.
Rabbi Yosef Messas (Otzar Hamichtavim, vol. III, § 1843) writes that if a child is donning Tefillin, then he can certainly be counted towards a Minyan, and said that he witnessed this practice during his time in Algeria. Similarly, Rabbi Baruch Toledano (Kitzur Shulhan Aruch, § 12) says that when necessary a child may be counted towards a Minyan. Nevertheless, Rabbi Shalom Messas (Shemesh Umagen, vol. IV, § 17) rejects this position and says he never heard of such a concept. In any case, it should be noted that a child should never be counted towards a Minyan a priori, or on a consistent basis, but rather in a time of necessity.
Rabbi Ben Zion Abba Shaul (Or Lezion, vol. II, ch. 5, §4) says that if one finds oneself in a Minyan that includes a minor, one may answer “Amen” to the blessings of the Amida or to Kaddish and the like, since there are opinions which support including a minor. On the other hand, Rabbi Ovadia Yosef (Yabia Omer, vol. IX, § 120:33), consistent with his position of not answering “Amen” to things that are counter to his Halachic methodology, says that categorically that one should not respond “Amen” in such a Minyan.
Summary: There were places that were lenient that a minor who is at least six years old and knows that it is Hashem Who is being prayed to, may be counted towards a Minyan. An adult who is part of such a Minyan may answer “Amen” and any other responses that are recited among a Minyan.