My ten-year old nephew asked my what I was doing for a living because he likes math and wants to do the same... and boy it's great but he looked at my scribbles and I'm not sure I'm up to the task.

What are good suggestions to explain interesting CS/math/algos to a kid?

I tried Zeno's paradox (after he saw the symbol for an infinite sum), but that may be a bit much to start (though he enjoyed it?)
Also discussed the drunkard's walk (what are his odds to reach his school if he walks randomly), but I don't think I did a good job at the 2D/3D thing