Q. When you call to the Torah on Simchas Torah a minor that is a cohen, does he get a second aliya if there is no minor levy?

A. Mishna Berura (282: 12) quotes Magen Avrohom that we are not obliged to call a minor who is a cohen to the reading of the Torah since there is no mitzva of vekidashto or honoring a cohen not yet bar mitzva, since the posuk (Vayikra 21: 8) clearly mentions that “You shall sanctify him, for he offers up the food offerings of your G-d; he shall be holy to you,” and that obviously refers to a cohen who is of age. However, Mishna Berura does quote dissenting opinions but mentions that our minhag is not call normally a minor as a cohen.
Horav Shlomo Miller’s Shlit’a opinion is that on Simchas Torah a minor can be given a first aliya at the repetition of the reading, (see prior question), but if there is no levy present he does not repeat, as we would normally do with a grown cohen.

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