The chances of getting them out by teaching them swimming/diving will have to be a last resort. I am an experienced swimmer with a little diving experience but I don't think I could make that swim. Muddy water, rocks and narrows, fast currents and all happening in the dark? would you do it?

As a non-swimmer and a child that has no concept of what will happen if you do panic I reckon there is next to zero chance of them or the accompanying divers getting through alive.

I hope I'm wrong but it could lead to a lot more deaths if I am right.

If they can get the water level low enough so that any swims/floats are minimal and in wider tunnels them maybe it will be worth a shot.