I find 12 years is probably the WORST age for starting a previously unknown technical activity. I have seen sons of farmers, instead, driving carefully a big tractor at 8 years old. A much better age for this than 12...
In reality they did a lot of useful activity inside this warm pool, specifically built for small children (6 months to 3 years) in the town of Reggio Emilia.
The instructor supervising this activity was named Roberta, and she was probably a completely crazy girl.
She asked the parent dealing with each child to do a lot of funny stuff, as pushing the 6-months baby underwater and keeping him/her down for 10-15 seconds. Pushing it to the bottom and watching him to resurface "swimming". Launching him in water form an height of 1 meter. At one year, those children were swimming autonomously thanks to small buoyancy devices inserted on their arms, albeit most of them were nit able yet to walk. They had to play games retrieving objects, initially floating objects, (so they had to swim) and later heavy objects, so they had to dive to the bottom of the pool, removing the buoyancy devices...
Around 1.5 years they were introduced to using fins, mask and snorkel, without those buoyancy devices, so they became "snorkelers". They also started to learn ear and mask equalization, albeit the limited depth was not really necessitating this. Around 2 years they had their first air tank. Initially the tank was on the bottom, they had to go down, retrieve the reg, make a some full breathings, spit the reg and resurface while exhaling.
They did drink a lot of water doing this, before learning that you need first to exhale for evacuating water form the reg!
Then they had the tank strapped on their back, and they did learn to swim underwater, they had to never touch the bottom, nor the surface. Roberta was particularly severe about the kicking style, making any sort of bad joke to children who did flex their legs or hit the surface with their fins...
Towards the end of this course, when the children were close to 3 years, she started a new game, using a large "plastic castle" submerged in the pool. This was made of several rooms, some with a roof (so you was trapped inside a box without access to the surface) and other with open ceiling (so you could breath above water). The rooms were connected each other with horizontal plastic tubes, entirely submerged, where the children could barely swim through. First the children explored the underwater castle using the air tank, so entering rooms without air above was not a problem. Then they had to to do the same, retrieving small toys hidden in the rooms, while freediving. This was indeed quite dangerous, a couple of times some baby remained trapped inside one of these rooms with the roof, and Roberta had to quickly savage them opening the ceiling (which was possible from outside, but not from inside).
She was really a crazy girl, my wife had some row with her, as my wife was worried of the danger of some of the games.
At 3 year, we moved to a deeper pool, in Montecchio Emilia, and now there was no need anymore of a supervising instructor, as my wife is qualified for babies 3 years and above.
So there we had the possibility to step up to more serious training: removal and evacuation of the mask and of the reg (also simultaneously), buddy breathing with a single reg, and those technical exercises which were standard when we started diving in the seventies, such as the "duck dive", the wheel, the square ascent, the horizontal translations with hand opposition, etc.
And of course breathing control, buoyancy control (using the lungs, not the BCD), etc...
This was an Olympic pool, in its deepest part it was around 4m. It did take almost one year before we did bring them in this deep part. And only after almost two years of training in this pool we allowed them to dive with us in the sea!
