I had thought I might buy the necessary material and write out the required instructions to do this and give them to three six and seven year olds for them to a

I had thought I might buy the necessary material and write out the required instructions to do this and give them to three six and seven year olds for them to assemble and launch (with adult help to carry the tank & fill the balloon). So far their mothers say yes, they have a sense of humour & don't think I will actually let the kids do it without a lot of help. Their fathers say no, likely because of their own selfish lack of input in building it and they think they might have to pay for the project (ie the damages if it goes wrong). I will have to try some more and hopefully in a few weeks will have convinced them to try this experiment.