The last few times when I have been to the American Express Centurion Lounge in San Francisco they would allow two children as guests (with one card holder) on an ‘exceptional basis’.
Today this wasn’t an issue at all and they uber friendly lounge attendant noted there is a new lounge access policy:
What is the guest policy?
Centurion® Members and Platinum Card® Members who receive complimentary access may enter with either up to two guests or immediate family (spouse or domestic partner, and children under 18) at no additional charge. Guest or family access is per Card Member, not per Card. Family and guests may not enter or remain in the lounge unless accompanied in the lounge by the Card Member.
If you purchase a one-day pass, your children under 18 may accompany you at no additional charge. You must purchase a one-day pass for any additional guests.
I’m not sure that’s really new but it’s a great benefit if you are traveling with the whole family.