Yes, however the license on it must be GPL, as the original theme is GPL and the child theme is a derivative work from it. Therefore the GPL’s derivative work clause applies, and the license for the child must be GPL.
But yes, the GPL does not prohibit selling a work, as long as you abide by the terms of the license.
Reference:
https://www.gnu.org/licenses/gpl-faq.html#DoesTheGPLAllowMoney
Does the GPL allow me to sell copies of the program for money?
Yes, the GPL allows everyone to do this. The
right to sell copies is part of the definition of free software.
Except in one special situation, there is no limit on what price you
can charge. (The one exception is the required written offer to
provide source code that must accompany binary-only release.)