Q. Can a minor read the Torah when he is given an aliya on Simchas Torah (just that portion)?

A. Shulchan Aruch (O.H. 282: 2) rules that you can call to the reading of the Torah many olyim, even if one repeats what the other one already read and is allowed to recite a brocho on it. Remoh (ibid.) maintains that in our countries the minhag is to do so only on Simchas Torah. On the next seif (3) the Mechaver adds that a minor who understands the meaning of the blessing, may also be called.
Therefore, Horav Shlomo Miller’s Shlit’a opinion is that once the reading of the Torah has been correctly done and the attending mispalelim have complied with the mitzva of listening to the Torah reading, a minor can be summoned to repeat and read the Torah again if he is capable.

Rabbi A. Bartfeld as revised by Horav Shlomo Miller Shlit’a