Corrected sentence: "What do pots start as before they are hardened in the oven?"
A slightly better version is: "What are pots made from before they are hardened in the oven (kiln)?"
Simple answer for a 6-year-old:
- Pots start as soft clay — it feels like playdough or mud.
- A person called a potter shapes the clay into a pot by hand or on a pottery wheel.
- When the pot is partly dry, it goes into a very hot oven called a kiln. The kiln "fires" the clay and makes it hard.
- Sometimes the pot gets a shiny coat called glaze and is fired again so it becomes smooth and waterproof.
Why I changed the grammar: The phrase "made harder" is okay, but "hardened" or "made hard" sounds more natural. Also saying "kiln (a very hot oven)" helps explain that potters use a special oven, not a kitchen oven.