Husky mom Koi are not really tank fish, they are pond fish. A kiddie pool would be useless with all the stuff needed to keep the water clean. Those fish can poop more than you can imagine in one day. Everything you need to keep the pond clean is expensive as well. Not to mention everything else neede to keep the water at right temp and oxygen levels just so. Rehoming as everyone suggested is the best thing for the fish in the long run. And can you imagine the room you need to keep a kiddie pool indoors. And if it springs a leak what happens? Too many ifs to be safe. Why take a chance on finding the fish dead? Koi are jumpers, they can jump right out of a tank, let alone a kiddie pool.