Without knowing the crosses or not that were used to create these chicks there is no way to assert that the birds shown are BSL. There are many breeds and crosses that can have this same appearance without being sex linked birds. Given the reported age and the significant development it is very unlikely that these are black sex link pullets.The Black ones are Black Sex Links. The ones with reddish markings are roosters and the white ones may be as well. The last one is a Red Sex Link hen. I have both as well as Buffs, EE, Mixes, Welsummers, and Rhode Island Red. No Leghorns sadly.