I explained this to my oldest when he learned about the steam engine and how cool it was. When I told him it was the peak in power he was like "but we have nuclear and gas" and I told him that nuclear power is basically just a super charged steam engine, and nuclear rods boil water better than coal or gasoline, but it's basically a steam engine. I went over how gasoline in cars was basically the same, but instead of steam, it used tiny explosions. We watched a few how it's made type videos.
I think it's up to 6 now.
Edit: yup, 6. https://www.cnn.com/2026/03/02/politics/six-soldiers-killed-in-iranian-strike-kuwait