I always put crumb and water right next to a sitting duck. My reasoning is that she might sit for 2-3 days on any eggs that didn't hatch by which time the ducklings would be very hungry. I doubt they'd be able to wonder outside to eat and find their way back. I also keep mine under cover for 4 weeks, in a run away from the other ducks, just to protect them from magpies etc. I wouldn't allow the /duckducklings in with other ducks either, I find that the boys will pounce on her as soon as they see her and she could run off and leave the ducklings.