Baby Ferret Trouble!?

My female ferret gave birth two weeks ago and I have recently noticed that the mother is ignoring one of the young the kit is constantly calling out loudly (I am not sure if she gave birth to additional kits because i haven't disturbed the nest but I only hear one kit) and sometimes I even find him venturing outside the nest but the mother just ignores him, is this normal ? If not what steps should I take to ensure that the kit survives ?