Or the trips to the zoo Aunty Jane used to take her on.
So before you launch into a discussion of the ins and outs of cryonic suspension, life extension and the like, check that you have correctly identified the problem.
In general, if a child is worried, try to find out what the worry is, so that you can address it as directly as possible.
Tia might be interested to learn about the ways scientists are trying to solve the death problem, and it might make sense to point out to her that it seems likely that by the time she is an old person, our lifespan will have been extended considerably by all the advancements in medicine, etc.
Another thing you might want to do, if your child is thinking about death, might be to read her a book such as , by James Halperin, or if she is a bit young to enjoy that, you could tell her about it, or retell the pertinent parts of the story, or tell her about cryonic biostasis.
As such, I keep looking up research on the aging process, that ticking clock that serves as the final limit on our lives.
As much as we've proven our ability to overcome injury and disease, aging is still with us, and until that ultimate time limit no longer plagues us, we'll never be free to live until we tire of living, which is, ultimately, what indefinate lifespan is all about.