How and when does Helen Keller's family first discover that she can neither hear nor see?

When Helen was nearly two years old, she became seriously ill. For the first nineteen months of her life, Helen had been a very healthy child. But early in January of 1882, she was suddenly struck down by a mystery illness—probably rubella or scarlet fever. Although Helen's fever soon broke, it became clear to her family that there was something seriously wrong with her sight and hearing. Mrs. Keller noticed that her daughter showed no reaction when the dinner bell was rung or a hand was waved in front of her face. It was obvious that Helen was now completely deaf and blind.
Helen's parents didn't know how to handle their daughter's condition. Trapped in a world of silence and darkness, she became wild and unruly, throwing tantrums as she became more and more frustrated at her inability to communicate. The common fate of children like Helen in those days was to be sent to a psychiatric institution. Thankfully, however, Helen's family discovered Annie Sullivan, a gifted young educator who would change Helen's life for the better and allow her famous pupil to establish a connection with the world around her.

When Helen first woke from the illness which took her senses from her, it was not apparent to either the doctor or her family that she would never see or hear again—they were just happy to know that she was alive and had survived the illness. Helen does not recall or mention a specific moment when her family came to realize that she was deaf and blind. She remembers that after her illness, she and her mother were able to make themselves understood to each other using signs and touch. She describes her mother as being the light in her "long night," taking care to help her daughter learn to do ordinary things, such as fold clothes, and reading her signs for food and even particular foods, such as ice cream. Evidently, then, Helen's parents realized quickly after the illness had passed that their daughter was both deaf and blind, but Helen does not recall a particular moment of revelation, either for herself or for them.