Hmmm, I just read some about them -- they're dual purpose, apparently? That would make sense because s/he is *huge* compared to the others the same age. We've been confused because this one really seems built differently than all the rest, very noticeably heavier. I think you're on to something. :)
Tractor Supply/Hoover's Hatchery, their "brown and white egg layer" mix. Supposedly may include the following breeds: ISA Brown, Amberlink, California White, White Leghorn, Production Red, Black Sex Link, and Rhode Island Red... But I'm pretty sure one of them is a golden laced Wyandotte, so I...
This is Mushroom (my 4-year-old says this is a great gender-neutral name, fyi). I posted pictures of him as a baby, but no one could really tell the breed, though everyone guessed boy. About 7 weeks old now and we're really curious!
You might get more help if you post this in the forum for breed and gender questions: https://www.backyardchickens.com/forums/what-breed-or-gender-is-this.15/
As a total novice, it looks like two boys and a girl to me...but don't take my word for it. :)
Here are updated pictures of everybody. They're a little over 3 weeks now. The one I'm most suspicious of being a boy is #5... They're all less cooperative for photos. 😂
They're still babies, but I'm really interested to know what more experienced folks think. My husband got them from Tractor Supply; 5 red sex links and these 5 mystery chicks. Did my best to get clear pictures, but I can take more.