I would get a pile of rubber duckies for DD's pool, the real deal poops, a lot, in the water. The cuteness is gone after about 5 minutes with that first mid-swim poop. With Bantam hens, you for sure need a female duck. A male, if he thinks he's a chicken, will treat the hens like his girlfriends. Not good.
You would also need a baby duck, and it's hard to get them sexed. Ducks are suspicious, thrive on routine, and hate changes. An older duck will not take to your idea very well at all. If your chickens are older (even by only weeks) they will pick at it or be mean to it. So, you need a companion to brood with it. Either another duck, a chick, or you yourself toting it around. Lot's of people have single ducks, but it's labor intensive compared to a chickens.
You'll need a plan for water management. I go through 7 gallons of drinking water every 2 days for 5 ducks. They throw it everywhere and will make a mudpit around the waterer outside. Inside, I made a catch pan by building a wooden frame, setting a flat under-the-bed type tote inside it, and covered it with rabbit wire. I can lift the frame to remove the tote to dump it. The waterer sets in the middle, and all the waste water falls in the tote instead of drenching the bedding.
If you decide after several months the duck thing isn't working out, you'll have one angry duck in for a rude awakening when it gets to a new duck home. I've been on the receiving end of this situation, a duck that thought he was a poodle. He was NOT happy. I even had 5 girlfriends for him, and he was still completely bent out of shape the first 2 weeks. He was so afraid and stressed. I had to pen him up separate but next to the girls. Took him awhile to lose his fear and realize he was in fact a duck. The day he realized he had 5 girlfriends was a riot though. It was like something clicked in his mind, the great duck epiphany.
