Injured newborn kit! Help! Graphic photos attached..

Hi
Our rabbit gave birth last night/this morning. When I went and found the new babies 1 was lovely and healthy.. the other not so much. Looks like it's head may have been sliced open by mum's nail or something? Definitely the smaller of the two that were born.

What should I do? Just leave it and see how it goes? Or end it's pain?
(First time having new baby rabbits in our house!)