Need Advice!

Ok, so my female cat just had her kittens March 19th. They are all healthy, fat and eyes are open. She had 4 total, one black, 2 grey (with tortishell splotches), and one orange. For some reason she keeps separating the black one from the rest. She doesn't take it from the closet and leave it though. She takes the black one under the bed and stays with it while leaving the others in the closet. I was thinking of getting some milk replacement milk for them if someone is going wrong with mom. Any ideas why she is doing this?

Ok, she tried moving another kitten so I am guessing she just wanted them under the bed. I was really freaking out lol.

Maybe the little guy needed some extra TLC...or she just wants to move them for a change.