My 10-year-old wants to know: “If earth was a grain of sand, how big would each atom be - basketball sized, baseball sized, grain of sand sized?” He eagerly awaits :-)

There is no good answer to this. But there are a number of videos that will show the comparative size of everything from a Planck Length to the visible universe.

Here is one. It might be much for a 10-year-old by himself, but if you have any science background, you can explain. It's pretty entertaining and it has dinosaurs too!

All I can say as to your original question is that it's estimated that one grain of sand has 10^19 atoms. That's more atoms in a grain of sand than stars in the universe. So even if the Earth were "one grain of sand" the atoms would probably be still very small.

But take that with a grain of sand. I'm not a physicist...

/r/AskPhysics Thread