Help!! does any one know what i can do if my rabbit is not feeding one of her littler?

I currently have a litter of 7 rabbits 6 of them are perfectly fine but one is obviously not being fed, the skin is very loose and it is cold. i found it today away from the rest of the litter outside of the hutch in the run, but mother simply ignores it, it is tiny in comparison to its siblings, i did pick it up and put back with the rest the others to try and warm it up however is there any thing i can do about the feeding, have read that it is very difficult to hand rear. do not want to hold mother down and comprimise her stopping feeding the rest!! if it helps they are 6 days old today!!if any one could please help i would be much grateful