help please!! ducklings hatched- one was found cold but alive 2 yards from nest laying almost dead

[Trimpkey]

My mallard duck has just hatched her first lot of babies. I went to check on her and found a cold but still alive duckling about 2 yards from the little kennel where her nest is. Mom came out of the nest and I saw a couple of others had also hatched and were alive. I put the cold but alive one back in the nest and she is sitting on them again. I have put a shallow water bowl out for them and some crumble duck food. The drake is standing guard.
I don't understand why one duckling was so far away from the nest? How did it get there?
Do I just leave things be? The weather is warm today in Virginia. (85 degrees).
I have raised chickens and know a lot- but ducks- am feeling very inexperienced.
Do the ducklings just stay in the nest under mom for a while? When can they walk?

Thank you!

 

[ChickenCanoe]

They can walk right away. I imagine it wandered off and got chilled.
I'd leave things be and just keep an eye on them. If they're just hatching now, it won't hurt them to eat and drink but they don't need to the first day or 2.

 

[Trimpkey]

Ok. They are all under the mother right now- chirping and popping their heads out. The drake is sitting outside the kennel standing guard however I'm wondering if he took the duckling out? He tried to peck at one under the mother but is now sitting again. We don't want to assume he'll be aggressive but also can't be watching him constantly.