Are they acting okay. have some activated charcoal on hand just in case. Or be proactive and go ahead and do a flush. in case you need it
https://www.backyardchickens.com/threads/flushes-for-aiding-in-toxin-removal.700526/
Looks to big a poop to be from a duckling unless they all pooped at once in the same place.
No blueberries?If not I have no idea what would cause blue/turquoise poop. But if they are foraging around the property then that could mean they ate something that caused it.