Financial Gift from a Foreign Bank Transfer

My mother is a dual citizen of both the U.S. and Mexico (born in Mexico became a U.S. citizen later in life). She recently sold land she owned in Mexico and the money from the sale is in her Mexico bank. She wants to distribute equal portions of the sale as gifts to her children that are all U.S. citizens, reside in the U.S., and have U.S. banks. Is this taxable or is it not?

 

Thanks in advance for the help with this question!