We talked for a while about food and energy and calories, but also about how it's not actually that simple, and about how different people start out with different body types. How my youngest sister eats more than I do, but is very thin, for example. Kavi wanted to know what kind of body Kavi had (I said medium), and if she could make it smaller. I said yes, she could try, but that it'd probably mean not eating enough, and then being hungry a lot, and feeling weak, and if she did that a lot, then we'd have to go to the doctor and talk about how to take better care of her body.
I ended up opening up the Sports Illustrated Body issue photos, and we looked at several different athletes' bodies and talked about how the shot-putter's body had strong arms and back muscles, how the tennis player had strong leg muscles, so she could move fast on the court. And I ended by saying that as long as Kavi ate good food and stayed active, her body would mostly take care of keeping itself healthy and fit. She seemed okay with that.
So that's the conversation at age 8 (with Anand, age almost-6, listening in somewhat). I foresee many iterations of it to come. Not sure I handled it perfectly, but not terribly either, I think. We'll see.