I don't know if the mother rabbit would come back for her baby, even if they left. Even if she was going to, they would probably assume she had abandoned it, since mother rabbits leave their babies alone all day, and come back in the evening after the sun has gone down.
Interesting how they refer to the bunny as "he" until she gives birth, after which point they refer to her as "it." There's probably a Tumblr-worthy thesis in culturally-prescribed gender assumptions in there.