When do you tell a young child about your memory impairment?

(Chapter 23 Living with a memory impairment and being a Nana in my book)

I guess my answer to this question is when they are old enough to understand and they might even notice the memory problems someone is having. My twin granddaughters are only fifteen months old, so it will be a while before I will have a conversation with them. I think that I will know when the time is right for me to talk to them about my memory problems.