itty bitty runt baby bunny

Question
Kiersten,
I haven't a clue on what type of bunny I just got is but it doesn't matter in this case. I picked up his little guy yesterday afternoon the women I picked him up from claimed he was 4 weeks old and that he was the runt she had another one she claimed was from the same litter that was much bigger and an older brother that was 8 weeks old that I took home too I picked up puppy formula for this baby and as the evening went on became much more successful with feed in fact it ate a lot off a Tupperware lid this baby is skin and bones and smaller than the palm of my hand so after it was done eating and his belly was full I was very excited then I believed he was constipated although hes had a few droppings. I had it separated from its brother whom is in a cage with our guinea pig and this baby I've kept in a shoe box which has holes on the top and I have been opening through out the night then I woke up to it I think in a panic it was hitting walls and laying on its side so I've picked it up and calmed it down and now have him on my chest with his brother he seems tired now I will not move them until I receive an e-mail from you. Hopefully you know what I should do. Thank you for your time.   
                                  Kristin

Answer
Hi,

THe bad news is that is sounds more like a peanut to me which means that it will for deffinite die.  But also if they are runts ten I would put them into a wodden box filled with hay becae this will seem like a nest to them.  I hope I can helpand good luck with your bunnies!