I worked with children with ages 10 and up in groups of up to 10 children. There were many years no serious burns. Only a few small blisters, because the children anfassten the hot workpieces too early.
It is important that the oven  on a generously sized, fireproof surface stand, and that the ground around the furnace is fireproof.

Hi. What is the minimum age that you would let your son or daughter use a typical muffle enameling kiln for small items? Of course, these kilns are red hot inside and when you take out your work it's red hot too. One has to be careful and responsible.