Grammar correction: Your sentence "What do pots start as before they are made hard in the oven?" is understandable. A clearer way to say it is: "What are pots made from before they are hardened in the oven?" or even simpler: "What are pots made from before they are baked?"
Answer for a 6-year-old:
- Pots start as clay. Clay is soft and squishy, a bit like play-dough.
- A potter (the person who makes pots) shapes the clay by hand or on a spinning wheel to make cups, bowls, or pots.
- Next the clay is left to dry so it is not too wet.
- Then the pot is put into a very hot oven called a kiln. The hot kiln makes the clay hard — this is called firing.
- Sometimes the pot is painted with a shiny coat called glaze and fired again so it becomes colorful and smooth.
So, in short: pots start as soft clay, and the kiln (hot oven) makes them hard.