Size of/info on bantam cochins?

Hi Everyone,
I bought 3 cochins (on accident) and have been expecting them to get huge according to what I have read online about them. However, they are all half the size of my barred rock, silver wyandotte, and americauna that are all the same age so I thought my cochins may actually be bantams. My question is, how big will they get? I haven't been able to find much info online so I thought someone on here might have some. I have read that they are great birds to have though and I will be thrilled with having some smaller birds (I wasn't excited about the idea of giant chickens who don't lay much). Any info would be appreciated. Also, for those of you who have them, how are they regarding laying? How old were they when they began laying? etc.
Thanks Everyone!