The context is that I'm an engineer and she wanted to know what I learned in engineering school, so I said calculus. (In my case, I only made it to pre-calc in highschool.) I swear I'm not the type of parent to try and push this stuff on her. I said it's about understanding how things change and then I tried to illustrate it. I'm open to suggestions on how I could answer her better.
Explain the difference between coasting on a bike and pedaling. When you pedal, you speed up. Calculus compares how much faster one person speeds up than another.
At 5, she's not going to grasp charts or numbers, but something familiar to her could work.
Source: father of three and taught my oldest basic algebra (variables) so we could make a game on Scratch together when he was 6 or so.
My mom was going for a math degree when I was around that age. I was naturally curious about what she was studying. What stuck with me though has been ways of thinking and concepts. It has been a really good thing for me in real life as well as academically.
My suggestion would be to focus on concepts and lean hard on why. The practical 'how' is something that takes lots of time to learn and is incremental (addition then subtraction and so on). The why can be highlighted in movement, natural shapes, thoughts on time/light/infinity, and things like that.
Calculus specifically I would approach by asking how many sides does a ball have. Is it one, zero, or too many to count? The 'right' answer doesn't matter in this context. The important part is to learn that they all kind of mean the same thing if you think about them in different ways. Calculus uses thinking about it as too many to count to answer questions that are hard to answer when you think about it as zero.