Mallard ducklings flipping over and dying

[I love my ducks34]

Ok, so this hasn't ever happened to me, but my dad's family used to hatch mallard ducklings. Over time they hatched a lot of baby ducklings but only one batch survived. The other ducklings would flip over on their backs and die. So this isn't an emergency, just an unsolved mystery, and if it's possible to prevent in the mallard ducklings I currently have. Thanks all! Sorry if this sounded confusing!

 

[Miss Lydia]

How old are your Mallards? How old were your dads ducklings when they died. What was he feeding them? Brooding them? Many things can cause this. Incubation to feed to the way they were brooded.

 

[Isaac 0]

Could have been a yolk sac infection.