donrae
Rest in Peace -2017

You can sex those chicks as soon as they're dry. The males will have a white/cream head spot, this is linked to the barring gene. Females will have a solid dark head.
whoops, sorry. You said the Cornish hen hatched the eggs....if they're hers, you'll have to wait. I was still thinking of the Cornish rooster over the barred Rock hens. Brain Fart

I agree the black sex link (your little barred cockerel) roosters make fun backyard breeders. I had one for about 4 years and loved his babies. They throw half barred, half non-barred chicks regardless of gender. A lot of black, but since they have the genes from the other parent (and in your case, some lacing from the Cornish), you can get some fun funky patterns in the offspring chicks.