[last_one_in]

OP here. Thanks! Will be testing with my 6 year old later. He actually hasn't seen it yet. Yeah, I agree. I wanted something that everyone can read and where the physical size of the number on the screen gives a great idea of the size (in terms of order of magnitude). Alignment is a great idea. I'll have a think about that one.

[tokamak-teapot]

    4,200,000,000 (4.2 billion)  
        1,000,000 (1 million)
          900,000 (900 thousand)

This kind of formatting would be great - for kids learning about bigger numbers and their names.

[last_one_in]

Oooo, I like that. That's really clear.