Whatever you may have heard, Thai women are very modest. Swim-wear for women here ranges from rare bikinis to common cover-all suits with half sleeves and knee length covering. Then add lots of swim caps and goggles. Very young girls usually wear suits with skirts.
Very young children are a special case. Many of them in the pool of my condo building wear life preservers, this to go into a wading pool with their mom seven feet away. Often they wear what looks like a wet suit, ankle and wrist length, total coverage, usually with the cap and goggles, often with the life preserver too. They look comfortable though, they’re having fun.
Most Thais have never gone swimming. Some have splashed around in irrigation canals. Things live in the rivers, things that make it a bad idea to swim. Not like alligators or piranhas, things with names like “liver flukes.” Tiny things that swim up a person’s urethra. And most places have no public pools, and hotel pools, although sometimes open to the public, are too expensive for most Thais. Swimming here is a luxury.
So the Thai people in my luxury condo building, those who have children, take them to swim dressed in every available swim gear, everything that they can find at the best malls in Bangkok. Just the swimming part is a status thing; the rest is icing on the cake.