With a wave from the lady at the wheel, the car pulled way, leaving the two brothers standing before the municipal pool. Neither of them particularly wanted to go swimming - it wasn't really the right weather for it - but with some pocket money in hand the two mustelids were wilfully bribed out of their bedroom.
The elder brother, a tall, grey-furred otter, lead the way in. His younger sibling tagged along, a narrower, smaller ferret. Passing into the warm, chlorine-scented building, it was a matter of waving their membership cards at the clerk - a red fox sitting at the reception desk with his head propped up on an arm. The most greeting he gave was an arm raised, pointing the way towards the male changing rooms.
Both the boys, drawstring bags slung over their shoulders, disappeared into changing stalls. The elder doing nothing more than stripping off his shorts and shirt and putting them safely away in his bag, his navy-blue swimming trunks slipped on at home before they left. Aside from grabbing a pair of goggles to keep chlorine out of his eyes, he stepped out to lock away his posessions.
He was ready to hit the water, but brotherly love meant that he had to wait for his slower sibling, who was only just pulling his swimming shorts on. With a quick ruffle of his headfur, the otter steps in to gather up his posessions, bundling his clothes around his shoes, and place them in another locker.
Both boys headed for the pool, the surface of which glinted as the sun peeked in through a skylight, high overhead. It was pracically abandoned. Apart from a few cubs recieving swimming lessons in the shallow end. No matter - the deep end of the pool called to the two strong swimmers, securing goggles behind their heads and over their eyes and standing on the edge of the pool...
"Raceyoutotheotherside." mumbled the ferret, leaning forward, curling his legs and diving into the water. The otter soon followed, eager to cut down the pretender's ill-gotten lead.
[...]
Despite themselves, and despite vocal complaints to their mother prior to leaving the house, both boys had fun. With the pool largely to themselves they ran riot, up and down the pool. It was only when the elder brother looked up at the time that he realised that all good things must come to an end - mom was on her way to collect them.
He beckoned his brother over. "We need to get going soon. Time for one more race?"
"Sure, but... I kinda need to pee first..."
The elder brother shook his head a little at the thought. Kids - always asking permission to use the bathroom! "Well, me too, but can't you wait until we've had one more?"
The ferret, treading water while the otter lay back against the edge of the pool, fidgeted. "N-no, I kinda have to go!"
With a roll of his eyes, the otter flicked a bit of water over at his brother. "Whatever. Just pee in the pool, I guess. I wanna win one more race..."
The ferret frowned, looking over his shoulder. The swimming lesson must have come to an end, the pool is abandoned. "Hrmf, fine..." He muttered, closing his eyes and trying to go.
The otter grinned a little. "Gross. Well, if you're doing it, I might as well, too..." Before, with a little effort, he manages to get a stream going, a strange warm feeling spreading across his groin. Sure, he'd peed in the pool before, but it still felt funny. With a tilt of his head, he pushed off the side and scooted away from his brother a little. He'd rather not be swimming in -that-...
Though, as he pushed away, he felt his paw slip against the side of the pool. Plunging a hand into the water to steady himself, he quickly found that he had almost no purchase on the water, and, without so much as a splash, he slipped under.
The otter wasn't particularly alarmed... Just a little confused. His reflexes kicked in and he slowly floated down a short distance to the bottom of the pool, his paws bumping off the tiled surface. He looked around and tried to swim up, but he found his legs mysteriously not complying, and his hands had no effect. Even stranger, he watched as his brother did the same, sinking to the bottom of the pool for seemingly no reason.
The two shared an underwater confused glance for a moment, though both of their eyes widened when they saw what was happening to the other.
It happened to the ferret first. The otter looked down at his brother's swimwear when it's colour started to shift. The aquamarine outer of his swimwear faded to white, and then turned almost totally transparent, exposing the net-like inner construction of the swimshorts. Shortly therafter, through the haze of faintly blue and faintly yellow water, they became skintight, shrinking down 'til they were skintight, expelling the water from around the ferret's crotch, and leaving the outline of his crotch clear to see through the netting of his shorts.
Soon enough, that too began to change. A spreading opacity formed to it, individual holes closing up and turning to plastic against the now quite dry fur of the confused, submerged mustelid. The otter squinted as colour started to appear on the white substrate, a purple-on-white pattern emerging from nowhere. Then, too, creeping in from the edges, colour appeared on the tight-fitting cover over the whole affair - a pattern of rubber ducklings fading in against a new, baby-blue backgroud.
It was incomprehensible. A cartoonish face appeared, emblazoning itself across the inner garment, which was now rapidly thickening, a summoned wad of fluffy, absorbent crystals puffing into being around the cub's nethers.
It twigged to the otter first. His brother's swimshorts were becoming an undeniably pair of cubbish diapers, encased in a snug, waterproof cover, and he was seemingly unaware! In fact, the younger brother's eyes were fixed firmly on the otter's speedos.
By the time the otter looked down, their change was all but complete. A perceptible thickeness was visible across the front of them, extending all the way down, between his legs and coming around across his bottom. The purple garment had risen somewhat, too, now almost covering the otter's belly button. Around the sides a pair of tearaway points had grown in. Now, with very little to show for the two full years he had on his brother, the otter modelled a carefully gender-neutral pair of swimmers. A swim diaper, no less.
The two stared at each other, a blush spreading across each of their cheeks. Neither of them knew how it had happened, but it was fairly clear what exactly it was retribution for. The ferret, a stream of bubbles escaping from his maw, reached down and ran a finger along the waistband of a very snug, tightly tied swimming cover.
Any further examination of either brother's clothing was suddenly interupted, however, as a pair of arms reached in from the water's surface, grasped each boy firmly by the nape of his neck and tugged them out of the water.
Bodily out of the water, even. As they emerged from the pool, neither would immediately notice the changes to their entire form - each was now far younger than when they had entered. The elder brother now a somewhat tubby 4 year old, the younger an wiry 3 year old.
The lifeguard, natrually, admonished both of them for going so far out of their depths, apparently oblivious to the ages of each before they had sank below the surface, and none the wiser to their childish attire. In fact, the lifeguard's only action was to take a hand of each kit, haul them to their feet and march them off the poolside... Right into the care of the swim instructor, who was busily helping the rest of her class out of their own swim diapers. That story will have to wait, however.