After finishing her description of her night with the children, the governess tells Mrs. Grose she believes the two children were meeting secretly with the ghosts of Quint and Miss Jessel. She tells Mrs. Grose that the children only seemed to be well-behaved and obedient—their goodness and innocence is “a policy and a fraud.” She says she believes the ghosts of Quint and Miss Jessel were encouraging the children to continue with the unspecified “evils” in which they had all partaken when the two were still alive and at Bly.
In this section the governess’s suspicion that the children are not truly innocent, but are somehow corrupted by Quint and Jessel, clearly escalates. Now the governess explicitly describes their innocence as a kind of mask for the "evils" they are actually practicing. Putting all this another way: the governess still sees it as her duty to save the children's innocence, but she sees herself as saving them from themselves as well as the two ghosts.
Mrs. Grose immediately accepts the governess’s evaluation of the situation, and, further, suggests that they must tell the children’s uncle right away and have the children removed from the estate. The governess refuses, and when Mrs. Grose says that she will then contact the uncle herself, the governess threatens to leave the estate. She is strongly committed to sorting out this situation on her own.
Mrs. Grose’s readiness to accept the governess's suspicions makes Mrs. Grose seem like a kind of enabler of the governess’s suspicions of the children. Mrs. Grose hasn’t seen the ghosts, but she fears them as a threat. Because Mrs. Grose is the governess’s only confidante, the governess’s suspicions are difficult to evaluate. At the same time, the governess wants to look competent in her job and is overawed by the rich uncle, and so she refuses to get help or any other outside perspective.