Size Difference in Polish Chicks of the same age

[RLynn]

First time Polish owner here. We got a buff laced polish and a white crested black polish chick about two weeks ago. Both are the exact same age and both started at the same size. Both are acting super normal, very energetic, eating, drinking, etc. the white crested black polish is half the size of the Buff Polish. Should I be concerned if the smaller one is acting normal? Or do some Polish just grow slower?

 

[TheOddOneOut]

Is it possible the small one is a bantam?