Can an underage child be questioned without one parents knowledge? Is the child supposed to be removed from the environment for questioning?

Two parents who have been divorced for sometime are now going back to court over custody of their 9 year old daughter. While being at the fathers house for visitations, someone came to question the daughter as to whether or not she liked being at her fathers house on one day, during this time her father tried to convince her to say yes she does. Meanwhile her mother was not informed that her daughter was being questioned. She found out via her daughter today. Can a minor be questioned without both parents knowing of the questioning taking place? If so are they not supposed to take the child out of the immediate environment where they are liable to be influenced by some factors? In this case the father trying to persuade his daughter to say yes that she does like being at his residence on mondays. The original settlement for custody was joint custody with the mother having permanent residence of the child, she sees her father every weekend and one other day of the week.