When I had ducklings (90% survival rate) I gave them a short swim every day. I waited until they were 1 week old before the first one though. Start by giving them about 10-15 min swim them gradually work up to them being able to have free range over the swimming pool by 4-6 wks of age. Given the current date I highly advise you to have them out of the brooder before 4 weeks of age, especially if you are putting an actual pool in. Once they are 3 weeks old I used to put them outside for about an hour somewhat unsupervised and give them a 30 minute swim before going in. Usually by this age they are pretty waterproof and can get out by themselves. Like I said in my original reply, the are hardier and develop faster than chickens. Be extra sure you don't overheat them. After 2 weeks you probably won't even need a heat lamp. I'd say as soon as the weather is averaging 50-60 degrees F you can put them in the coop full time. Over heating id one of the number 1 causes of death in young ducks. Learn to 'read' the ducks, if they are huddling together make it warmer, if they are panting take the heat lamp away. Above all, just follow your instincts, I can tell you are a good person that wants the absolute best for your ducks so just do what you think is right. In my experience I've found that you can do all the research and ask all the questions in the world, but when it comes down to it you usually end up following your instincts and learning from your ducks. Seriously, ducks are really strong and don't die easily, the only duckling I had die was 1 and it was b/c it was a runt and sick when it was shipped to us.
Happy to Help,
Bailey1204
P.S. I am only 13