Duckling suddenly died after the other had been bullying it

[tanithcrane]

Hello I hatched some ducklings a couple of days ago out of 4 eggs only two hatched one was born with a small deformity in its foot but after lots of care the duckling has doubled in size and become really strong but is limping a little we had its sibling who was also doing really well untill this morning it was found on its back and couldn't get its balance the other one was constantly picking on it and pecking its head we separated them and then the one that was being picked on suddenly died I'm so heartbroken and I keep thinking did I do something wrong I feel so raw
It did have a little tumble off my lap the other day but I checked it over and made sure it was OK i also kept an eye on it for most of the evening and it was sleeping under the heat lamp and would get up everytime I went over to the cage could of it sustained an injury?? I feel like it's all my fault

 

[BirdsBeesTrees]

It was probably failure to thrive and not because it fell off your lap.