It was a seam failure in the back of the tube. You know, where other boats will start the cone of the tube, not the very end, but where the rounded tube becomes the cone, that´s where SeaEagles have a rounded pontoon. That's where it happened. Basically several holes developed as the tube and the tube end seam fell apart (became unglued).
It was not repairable, I had to replace the complete hull. Hope this helps. If you've got more questions, email me.
I think if I had a punchure, we are generally fairly close to the shore, so should be ok.
I read that it always good to get your children used to the water and floating in there life jackets, so if something does happen its just like going for a swim and not a big panic.
I have thought about taking my out board off (when on my own, in shallow water) and letting a tube down just to see what happens, but this might be a bit extreme.