I'm not sure what they are. They look like they have leghorn in them with the giant combs. They for sure aren't a CornishX or white broiler, the different "brand names" change depending on what hatchery they come from. Those huge combs just keep screaming leghorn to me.
Here's a picture of one of my CornishX roosters at 6 weeks of age. He weighed about 7 lbs at that time, the other roos were a little bit smaller.
A white rock is not really a meat bird by todays standard, they just don't grow as quickly or get as big. The have normal sized legs and body while...
At 7 weeks, CornishX should be at least twice the size of your leghorns. They don't sound like broilers to me if they aren't big already. You might have White Plymouth Rocks.