I like all your designs, ang I would like to vbuild them all.
But are we not about to forget one thing? The kids were supposed to build their cats? The designes and solutions start to be far to complicated for kids say around 12 to build, even a chained hull is not so straight forward to set up.
I am not an expert in any way in boatbuilding, but I have been working with kids on both wood and metal and my experience is that it has to go fast and change all the time...