Ducks are the sweetest little hatchlings but by far the messiest. I wouldn't keep them in with the chicks -- too wet and too much poo. They can be in the same area but separate them with a screen or something.
Also, be sure to check not just for cracks if you're using commercial waterers but also for a bad seal around the base -- I bought a bunch of them this spring, and bought the plastic jars also since that way I thought I would avoid mason jars and the risk of glass breakage, but I found most of the plastic jars so loose fitting that the water would leak out in short order. So I had to switch to quart mason jars anyway.
Finally, not trying to lecture or be a know it all, but for the health of the birds they need to be kept clean. You really should change out their bedding at least twice a day, morning and evening. I found when they were young the best thing was pine bedding, even though they would eat a little of it. It is absorbent and helps keep odors down. You can get away with changing it out once a day and adding a fresh layer on top 12 hours later if you must -- I confess I did this a few times when I was running late for work in the mornings, but it's not ideal.
Best system is to have duplicate EVERYTHING -- storage bins, heat lamps, waterers, feed dispensers, etc., so you can just transfer everybody into a clean fresh bin, and then take the old one out to be cleaned for the next change in 12 hours.
