We lost a wee one today. He must have clung to his mother too tightly and been dragged out of the nestbox, because his little belly was absolutely full. Banjo, our Springer, discovered him when I went to feed the bunns. I thought I saw the little tail move, so I tried in vain to warm him up and resussitate him, to no avail.
Such is the world of bunnies. I have better nursery cages outside, I thought keeping Mom and babies inside would help prevent this, but baby bunnies are very delicate, and it doesn't take much to kill them, unfortunately.