According to the fact sheet, the new policy won't affect the following children:
Those whose parents are both U.S. citizens, with at least one parent who had a residence in the U.S. or its territories before the child was born;
Those who have two married parents, one of whom is a U.S. citizen who "was physically present in the U.S." or its territories for at least five years, with two of those years occurring after the parent was 14 years of age;
Those who have unmarried parents, one of whom is a U.S. citizen meeting requirements listed in U.S. statute INA 309;
Those who are eligible to have their U.S. citizenship certified at birth;
And those residing in the U.S. with their U.S. citizen parent after being admitted to the U.S. for permanent residence.