Sculpting is an excellent activity for people of all ages! Let me throw a few thoughts your way.
Air dry and oven dry clay is an affordable and forgiving direction to go with clay. It stands up well to beginners and gives more time to work. The turn around time between creation and dried/fired completion on air and oven clays is also much shorter and possibly a better match for those with shorter attention spans. Kiln clays have a balance of moisture going on where you need to move quick, they begin to crack fast and if you add water, that has to be done carefully/slowly or you just create more cracking. If you decide to go with kiln clay, I would highly recommend paper clay as it is more forgiving (available at Trinity Ceramics for ~$20 per 25#).
If they are making pieces to go into the kilns then you/they will need to be thinking about the construction. Solid items (balls) are tricky as they can trap moisture and if not completely dry, explode and take out other pieces in the kiln. Hollow forms are better. Thick pieces will need to dried for a very long time before going into the kiln for this same reason.
There is a scrap bin of clay in the Fired Arts area along the back wall labeled ‘Free Clay’ that you are welcome to use. It is a general cone 6 stoneware. As far as kiln use, the Firing Team handles the actual firing and there is no training necessary to put your pieces on the shelves to be fired. If you decide to go the kiln route, I can meet with you to go over suggestions to help make for a more successful venture! I would also recommend checking in with us on those first pieces before you shelf them to make sure they will hold up to firing and aren’t rejected for structural issues, etc.
As far as ‘kiln-worthy’, I have a pretty broad definition there, personally. My primary concerns are in the safety of other’s work and throughput/volume. As long as the pieces are safe and the number/size of items aren’t putting an undue strain on the system, and that’s the same for anyone having work fired, then it’s all good. Though I do want to warn that we try to fire as equitably and efficiently as possible and that sometimes means pieces take more time/less time to go through the process.
So! That was a lot of words to basically say: I’d personally recommend starting with air/oven dry, but if you are stoked about kiln work, I’ll absolutely help you out with that. Let me know!