Are the ducklings in with the chickens?
If they are, IMO you need to separate them. Ducklings can handle being wet a lot better then chicks and your chicks could get chilled due to the water the ducklings bring back on them.
I also prefer to keep the ducklings food dry, bacteria can grow fast in the warm air of a brooder, but I also make sure that my ducklings have lots of clean water every day.
I first I was worried about my ducklings being wet & cold too. So I gave them lots of water in a container that they could not swim in. Then once a day I would give them a warm bath in our tub. My hubby and son would watch over them, while I cleaned out their brooder box, then would slowly carry each one back in a towel to get off excess water. Of course I only have 2 ducklings so it wasn't that hard for me to do.
I have my 2 ducklings and 4 chicks that are in a fenced off "playground" outside and they are doing great, but at night they sleep separately because of the dampness of the ducks.