Normal
I would be careful not to equate old with dying. kids think 30 is old and you could end up making them fearful if they ever hear you or someone else say they are getting old. Say that grandma is very very sick. then talk to them about death in a natural non threating way. The key is to take the mystery out of dying. We fear most what we do not understand. There is a lovely book on this subject Occupational Therapist (OT) help children with death and dying it is called "The Fall of Freddie the Leaf" It is probably at your library but is available at Amazon.com also. I have used it myself and have given it to a few young mothers that found themselves in your position. It is a good way to get the conversation going.