Well this is somehow a step were I discovered, Few weeks back, I bought a cheap clay and its already hard and can't be molded right, so I search online on some tricks on how to make a hard clay to be soft again, and I've tried the first one that showed first in google, It says that you need to put it inside a plastic with water and put a hole around the clay and leave it for a day, guess what? It didn't work.
A then few days ago, my kids are playing clay outside and leave it in the table under the sun, and after an hour or so, I notice it and planned to clear the table , then tried to pick the clay but it is all so sticky and so soft.
So now, that's the trick, lol, Just let it sit under the sun for an hour or 2. Hope this one is handy to some parents or kids who love to play clay.