The nice thing that happened in class today:

Grade 5 students solve a puzzle where they put cuneiform numbers in order (there is no guidance, just work with the symbols, how do you order them?)

I told them they are like archeologists cracking a code. They did it!

"But where is zero?"
"It wasn't invented yet." I said this seriously. I mean ... it's true.

Later that day the same student asked if it was a joke. I got to tell them no! Zero had to be invented. Everything had to be invented!

This student wants to "invent a new zero" so. Watch out everyone. Math is about to get a lot more... IDK ... but MORE.
@futurebird but in seriousness, there is more actual mathematics in this question (can I have a second zero) than in all the calculations we do in school "maths".
Have them write down rules how to use and calculate with their new zero and have them check if they are consistent, and think about a way to check if indeed the two zeroes are truly different numbers, even if they fail to carry that all out, they'll learn a lot about the spirit of mathematics beyond the very limited confines of school "maths"