Math Provocation - Button grouping

I arranged this simple provocation with a bowl of buttons and muffin tin.

  "How many different ways can you group/sort these buttons?"

I was very curious to see what kind of answers Sid and Nidhi could come up with. 

First, Sid put one button in each cup.  I thought to myself "May be they don't get what grouping means?!"

Next, he started loading the cups with one more round of buttons.

Me: "What are you doing Sid?"
Sid: "I am doing it by numbers!"
Me: "Oh! Now I get it!"

Do you?

Shrini jumped in. "I can do it too!". Here is her way of grouping by numbers.

Is it not amazing how their little minds work? I thought they might go with the obvious color or size sort and they totally took me by surprise.

Also notice the elegance of this very open ended question. I am sure I ll be taken aback by a totally different answer the next time I present the same simple question to the kids.