@cjd @LukeAlmighty @Witch_Hunter_Siegfired For someone in 3rd grade asking that is smart, but an adult should have learned elementary chemistry

Ok then, since you certainly learned it in elementary chemistry, maybe you can explain it...

Why is it more likely that everything is made of tiny atoms as opposed to everything being made of solid stuff ?

You can't just hand-wave and say "chemistry", as if the fact that carbon burns in oxygen somehow proves that the carbon and the oxygen are made out of tiny little pieces as opposed to, say, solid globs.

Tell me how we know that we're not living in a world where all observable laws of nature are the same, but atoms don't exist.

@cjd @LukeAlmighty @Witch_Hunter_Siegfired It does actually

If they did not exist as fixed units they would not be elements like oxygen and carbon, everything would exist as some infinite gradation of stuff

The fact we can write equations like:
CH4 + 2O2 -> CO2 + 2H20
And get equivalent results proves there is no infinite gradation

Also, did you not learn about how atoms were proved and their properties were discovered with brownian motion in chemistry class? Stuff like moles or gas laws in general would make 0 sense without atoms

If you look in a microscope, everything is moving around even when everything is still. The warmer it gets, and the smaller the particles get, the more they move.

This is called Brownian motion, and it is explained by matter being made of particles that push against everything and when the matter is small enough the energy of individual particles is enough to jostle things around. It isn't the only proof, but it's good evidence that matter is made of molecules, and that heat is related to the movement of those particles.

It was Albert Einstein who described Brownian motion mathematically which was one of the major things which helped tip the consensus of scientists towards atomic theory rather than something else.

(I know, you weren't asking but I thought Brownian motion is pretty cool so I decided to share anyway)

No, that's exactly the question I was asking. I also asked GPT because I got curious and it gave a really excellent answer. It identified that and also X-Ray Crystallography which has a diffraction pattern consistent with regular arrangements of atoms.