I got one for them last year and all but one mare was terrified of it. She stood and pawed in it, which of course terrified the others more. She made a muddy mess and then rolled in the mud and then splashed some more. I ended up taking it down to the big barn and used it as a hay feeder for my big horses. Most of mine enjoy being misted with the hose when its really hot.
I haven't tried a kiddy pool, but do have a big rubber tub that is similar and I have filled that a few different times for different groups of horses. most aren't interested in it. Some of them like to play in the water when I've got the hose running to fill the tub (I'd spray their legs and bellies and then they'd try to lay down on the side of the tub and roll in the mud I created while spraying their legs and bellies. Once in awhile someone will paw at the tub & spill the water out, but mostly once the tub is full and I and the hose are gone, the horses lose interest & the tub just sits there. Sometimes someone will drink from it, but the water in their water tubs is fresher so I end up dumping the rubber tub and putting it away again.
When I was a kid I had friends who had a big old pig named Arnold, and Arnold liked to play in the kiddy pool that us kids wanted to splash in. By the time that pig got done with the little pool, it wasn't fit for us. Eeewwww.
WOW!!!!! I use them all the time, for babies. They love them! I double them up, as sometime there'll crack because of them pawing. This wy the bottom one till keeps the water in there. I have had them lay right down in them. I empty them at night so the mosqitoes stay away. I fill them back up in the morning while I'm feeding. Even some of the older horses enjoy them also. I have never had one afraid of it.
I have used them the last two years. All of my horses like it and are in it as soon as I put it out and start filling it but they get bored with it fast. The fun only lasts about a half hour or so and then it just becomes a slightly dirty watering tub. I usually end up dumping it out after a few days and then put the pool away for a week, when I bring it back out again it is the same fun for the same amount of time and we go through the routine again.
I don't use a kiddie pool,but I use a rubbermaid short tank for 1 mare.She was born in TN and I think there must have been a stream on the property where she lived.In the summer she will put both front feet in her water tub or trough and splash herself with her muzzle with water.In winter she will take her hoof and break ice for water(I have heated tubs now so she doesn't get the chance.)She is 1 mare who would survive in the wild.She is 20 now and still amazes me with her survival skills.She is W&L'DS TENNESSEE GAL, a BOND CHAUNCEY daughter.She loved her play pool.I don't worry about the dirty water.she has another tub for drinking and no longer plays in her drinking water.
I've got 4 out there right now. They love to drink out of it more than using their water troughs., and yes I have to clean them up daily but its no big deal.
They get in it and splash, paw, make a muddy mess, lay in them, roll around in them......you name it. They love it. Noelle is like her mother Dirty Holly who is such a drama queen and lays down in it and squeals like a pig. Sometimes I'll throw some carrots or apples in it on occasion. I also freeze milk jugs with water and toss a couple in them too so they stay a bit cooler longer. They definitely love their pools.