How long has it been since the momma gave birth? I stick my hands in the cage the first day- but if I know their very newly born, I give them a few hours. You want to look for big white milk bellies, if the ones in the other corners dont show anything soon - I would GENTLY pick them up and put them in the corner with the others. If the momma still refuses to feed them you should try rubbing some of the smelliest bedding from her cage onto them and placing them back into the corner. Although, it's natural for the mom to want to narrow down the litter size. Sometimes the babies will come out stilborn, or die after birth; you dont have anything to worry about.