Hen mean to black chicks

[henney penny]

Why would a hen pick at the black chicks,she has 11 babies and the rest are the buff color.In the picture you can see the two blacks up against the fence,when they try to follow her she pecks at them and when they scream for her she ignors them.She lets them sleep under her and allows them to eat but thats about it.They seem smaller than the others two,

 

[spaceranger]

Hi my Cochin hatched a set of eggs 2 weeks ago and loves her buff chicks but attacked the one black chick that hatched so I have her indoors with me, It's really odd isn't it! Wish I knew whether it was down to her being suprised by one odd chick?

 

[Eznet2u]

Sorry, couldn't help myself.