Now define distance :)
You can make this argument on literally any definition - you have to start with something.
So dictionary.com says the defintion of distance is:
> the extent or amount of space between two things, points, lines, etc.
That works for me.
I think it makes sense to start with something physical, in the real world that people - and especially kids, can intuatively understand. Our brains by default understand what distance is. Maybe that's true for numbers as well- and that's ok too.
Don't forget "continuous" and "line". :)
> In mathematics, a real number is a value of a continuous quantity that can represent a distance along a line
That's the intuitive definition that makes the most sense to me.