Hmm,that could be--I've been doing this long enough that I've probably forgotten some of the things I struggled with. It feels like it would work to say, "Here's this graph of a sine curve, and what that means is if you take a value you want to find the sin of on the X axis, and trace upwards until you get to the line, and then over to the Y axis, that's the sin of that X value [draw a couple of examples] and if you have a bunch of X values that you want to calculate the sin of, you can put them in an array A and use A.map(sin) and the result will be a new array with the corresponding sin values [draw input array A with the same values as the Xs selected on the graph, A.map(sin), and a new array with the corresponding Y values as from the graph]"

Sure, it won't work for everyone, but I'm guessing (hoping?) that "functions as first class citizens" won't seem that weird to people who have never worked with a language where they weren't

I think the hard part is trying to imagine 'run' combined with 'function'. If you present a picture of a collection of data, a function that maps input values to outputs, and a picture of the output collection of data, that's fairly easy to grasp. The difficulty comes from bothering to describe how the computer does it by running a first-class function on the data. And that's the part of understanding that could be delayed IMO. Treat more of programming as declarative rather than procedural.