Just as Alzheimer's disease is unique in each affected person, so are your children when it comes to discussions about the illness.
What you say to them and how you explain the disease process depends on their ages and levels of comprehension.
If they are too young to understand the biology of the disease, talk about illnesses with which they are familiar, such as chicken pox or measles. Explain that while these illnesses have physical signs, Alzheimer's is a sickness in the brain that no one can see. You can add that this illness can make people forget or sometimes get angry, but reassure them that their grandparent doesn't mean to act that way. Reinforce that it's OK for them to be sad or angry, and also make sure they know.
Reassure your children that no one caused the disease. There are children's books available that illustrate the disease process in a simple, age-related ways which might give your children. Some titles are: "What's Happening to Grandpa?" by Maria Shriver; "Nice to Meet You … Again: Empowering Children to Find Joy and Understanding in Loved Ones with Dementia" by Suzanne Bottum-Jones; "Sometimes Even Elephants Forget: A Story About Alzheimer's Disease for Young Children" by Kathleen Welch and "The Girl, the Star and the Spider" by Sherry Van Atta Smelley.
It is also important to show your children they can still talk to their grandparent and enjoy activities together. Playing music and singing along, doing simple arts and crafts projects and reading stories aloud are all examples of creative and enjoyable activities they can enjoy together.
These special times will make your children more comfortable with their grandparent, who also will get some socialization and external stimulation to help maintain their quality of life. They would both be strengthening their relationship in positive ways, and your children will gain a greater understanding of the disease process as well as develop compassion and empathy for their grandparent and for those who take care of them.
Your explanation of Alzheimer's, given the span of the disease, could become an ongoing process. Be sure to acknowledge any feelings or fears your children may be experiencing as they continue to witness the progression of the disease, and allow them to talk openly and freely about them.