I would certainly not allow it..unless they have another family member going...Today, there are sick people in the would that would take advantage of this situation...How can a 90 year old be responsible for the safety of an 11 year old girl...She could disapear in a flash....If it's a tour, the guides will not be with them every minute....
My granddaughter has traveled to different countries with her parents and my daughter said she didn't let her out of her sight...I'm not near 90 and i know my daughter wouldn't let me take her 11 year old out of the country without her...This is just my opinion....To day it's not safe to let kids roam the malls in this country...