Dunno why you lot think its so complicated.
More pumps. Get that water away faster.
And looking at the BBC diagram the whole thing isnt flooded, and some sections are only half flooded. The only bad bits is where they have to fully submerge.
Yes the visibility will be poor but powerful lights and guide ropes means you have to just pull yourself along.
Can totally understand the kids would be terrified using scuba gear, so would I. But they dont need to learn how to use it because they can have it all strapped on them and be fully supervised by a huge team. They can rest at interval stations for food whenever the cave system partially opens up again (it isnt all flooded).
I think there is one section where the tanks cant be worn on the back, but they should all be using pumped air feeds now not individual tanks imo.