Newborn bunnies possibly are orphans

I discovered a little burrow in my green onion patch. At first I thought it might be rats so I dug in and discovered newborn bunnies. I tried to patch my blunder and now just discovered there is a dead rabbit across the street. I'm worriedmthat it is these bunnies mum. What do I do if their mum doesn't show up and the dead one can be presumed to be their mum?

I feel absolutely horrible about disturbing the burrow and now even worse if they turn out to be orphans.