Your child will let you know how much information he needs by the nature of his questions. Answer candidly. At the same time, don't volunteer more than is necessary, such as details about what late-stage Alzheimer's can be like if your parent has only just been diagnosed and shows mild to moderate signs of impairment.
If a grandparent forgets your child's name, calls him by the wrong name, or confuses him with the childhood you, your child might misinterpret this mistake as evidence that Grandma doesn't love him any more. Explain that it's not that she doesn't love him; it's that she can't remember things that just happened, or even the names of people close to her. Young grandchildren's names, because they're more recently acquired memories, are often more quickly or easily forgotten than those of more lifelong acquaintances.
Another fear: Even if your child doesn't ask, let him know he can't "catch" Grandma's problem from being near her; it has nothing to do with germs.
