The Shulhan Aruch (O.H. 282:3) says that all are eligible to receive an Aliya, including women and minors. Although our Sages said that the custom is for women not to receive Aliyot out of respect for the congregation, the common custom among Sepharadim was to allow children to get any of the seven Aliyot.
The Magen Avraham (M.A., O.H. 282:6) discusses a case in which only a Kohen who is a minor is present in the congregation. In such a case, he explains, there is only an obligation to honor a Kohen who is thirteen years or older and therefore, it is preferable to give the first Aliya to an non-Kohen adult (that is, a Halachic adult who is thirteen or older) rather than to the Kohen minor. On the other hand, many Aharonim disagree with this position. Rabbi Shalom Messas (Shemesh Umagen, vol. I, O.H., § 40) and other Sephardic Poskim write that it is permissible to give the Aliyat Kohen to the Kohen Minor. When it comes to the weekday reading in which there are three Aliyot, the HIDA (Birke Yosef, 282:5) says that according to Kabbalah it is preferable that a minor not receive an Aliya but that there is not issue with Shabbat in which there are seven Olim. Although Halachcally permissible for a child to receive any of the seven Aliyot, it has become customary among Moroccans to honor children with only the Maftir reading.
Regarding actually reading the Torah, generally speaking, in order to fulfill a Mitzvah obligation on behalf of others, one must be an adult. Nevertheless, according to many Aharonim, strictly speaking, a minor may read the Torah on behalf of the congregation. This was the custom in Morocco and was pertinent when a child’s Bar Mitzvah was held before his thirteenth birthday, which was common. Nevertheless, Rabbi Avraham Amar (comments to Magen Avot O.H ibid) explains that his Bar Mitzvah was held early and his father (one of the prominent poskim of Meknes) re-read the Torah portion after his son so as to ensure that the congregation’s obligation was met. Summary: A minor may receive any Aliya to the Torah. Strictly speaking, a minor may read the Torah on behalf of the congregation