Is something wrong with my polish chick

[Valentin]

Hi so I have two Polish chicks the one on the right is a rooster and the one on the left is a hen so the rooster has not been growing as much as the hen I wondering if it’s OK they are the same exact age and recently the rooster has been getting poultry lice on its neck so I am treating with permethrin on that but could there be any other issue of it’s not growing and these are pictures of them when they were babies

 

[The Happster]

Probably the cockerel is bantam.

 

[Valentin]

Probably the cockerel is bantam.

Yes that’s what I thought but I remembered I got them from a breeder and the buff polish was a lot bigger than the blue polish when they were baby chicks