Ducklings suddenly dying and I can't figure out why

[AmbersOfNimbus]

Hello. I've been raising six ducklings as of late, who are around the age of around two and a half weeks old. However I've had them for around two weeks myself.
I've got medicated duckling food and I check their food and water multiple times a day, along with making sure their heat lamp isn't keeping them too hot.
However just an hour or so ago, I got them fresh water, as they were a bit low. I came back and suddenly three of them are on their sides, dead. I don't understand how this could've happened. Two of them were damp and the third was dry. They were active and seeming just fine an hour ago. I don't have any pictures currently however I can possibly obtain them later today, if needed. If anyone has any idea on what can cause them to suddenly do this, please let me know.

 

[Molpet]

Did you open a new bag of feed, change the light bulb, anything different?

 

[AmbersOfNimbus]

Did you open a new bag of feed, change the light bulb, anything different?

Nope. The only thing aside from new water, which was the same filtered well water I use for all of my birds, I had just recently changed their bedding, however it was the same bag of woodchips I'd used for them earlier this week.