What kind of chicken is this?

[Hyfly11]

Hey all! I'm new here and was wondering what kind of chicken this is. When I purchased I was told a Brown Leghorn. However, it is about 3 weeks old in this picture and the Black Sex Links are about 2 weeks old and much smaller. Is it a brown leghorn or something else?
Thanks for all of your input! This will be our first year with chickens and we're excited as both my wife and I grew up with them. Our kids are loving them!

 

[Chicken cas]

Are you sure of age? I have some about that size that are 4-6 weeks old. How do you keep it in the pool brooder? I have a tall tote and mine get out at that size/age just from flitting around and using waterer. I would run with brown leg horn as I think they grow a bit faster due to being dual purpose.

 

[Hyfly11]

They just stay in the pool. I am surprised also actually! I'm not 100% sure on age but we purchased the black sex links 8 days after the "brown leghorn" and they are supposedly fresh arrivals at the local store. So possibly a week and half older.
We purchased the brown leghorn 3 weeks ago tomorrow and the black sex links 2 weeks ago this coming Wednesday.