Okay kiddo, so a double exponential function is a special type of math function that looks like a curve or line on a graph. The reason it's called "double" is because it has two parts that are like an "exponential function".
Now an exponential function just means that it grows really fast. Let's say you have a number like 2, and you want to make it much larger. You could multiply it by itself a bunch of times, like 2x2=4, 4x2=8, 8x2=16, and so on. That's an exponential growth - it gets bigger and bigger by multiplying by the same number each time.
So a double exponential function is like two of those exponential things mushed together. It can look like a straight line or a curve depending on the numbers you use.
For example, if you take the number 2 and raise it to the power of another number, like 2^x, you get a exponential curve that gets really big really fast. And if you double that number and raise it to the power of x, like (2x2)^x, that's a double exponential curve that grows even faster!
Sometimes, people use double exponential functions to describe how quickly things grow or change over time. It's kind of like predicting how much money you'll have in your piggy bank if you keep adding a certain amount every day for a long time. But with more complicated math.
Does that make sense, kiddo?