No. The account belongs to your son, not to you. Sales in your son's account have to be reported on his own tax return, not on yours.
It would be a good idea to file a tax return for your son, even if he is not required to file, in order to establish the capital loss. It might not do him any good this year, but he can carry it over and it will reduce his taxable income in some future year or years. He should file a tax return every year until the loss is used up, to maintain the capital loss carryover.
