Although I don't have a kiln. I wonder if an outdoor pizza oven would work.
I have designed and made many pottery kilns and there are some rule of thumbs that help in knowing if the design will work.
A brick insulated kiln requires around 30,000 BTUs/cubic foot of internal kiln volume input.
A ceramic insulated kiln requires around 5,000 BTU/cubic foot of internal kiln volume input.
The kiln's flue needs to be sized around the kiln burner's input and needs to have 1 sq inch of flue area per 4,000 BTU/hr of burner input.
A weighted damper is placed over the flue outlet to adjust the flue area to create either a reducing or oxidising atmosphere within the kiln. The flue needs to be as square as possible to get the maximum flow through the flue as possible. I saw a flue designed by an insulation salesman which required a 12"sq flue so he made the flue 12" long by 1" wide and the flue would not draw properly and only created a reducing atmosphere within the kiln. The kiln design as built would not allow the kiln to be adjusted to produce an oxidising atmosphere as and when required. If the flue had been made 4"x3" in its cross section, it would have worked as either a reducing or and oxidising kiln.
It is possible for an expert potter to fire their wares in a few hours without breaking any of their pots etc., whereas a newbie, inexperienced potter, may a take couple of days to firer their clay wares because of the imperfections/weaknesses they leave in the pots while making them.
I would advise that you find a "professional" potter who is willing to teach the art of making ceramic wares and will use their own kiln to fire the pots etc. that have been made by their student potters. As the student potters' experiences expands, their skills in making better clay wares will also improve and they will have fewer failures in what they craft.
I would often tell potters that their best pots etc., were often the mistakes that survived in the kiln and could not be reproduced again. Because of the rarity of the surviving pots, they could command a high price to buy because they were truly unique.
Encourage your children to persist in their endeavours as they learn to become a potter. It really takes a lot of time to learn the art of shaping clay to end up with something of beauty.
Shalom