What kind of chicken are these?

[BantamLover21]

Maybe they're Sebright/Wyandotte bantam mixes? That would explain the larger size, but other similar Sebright traits.

 

[WyandotteIndeed]

Chickens are all one species in that they can interbreed and produce viable offspring, but generally are divided into "bantam" (which includes seabrights and most game fowl) and "large fowl" (LF are "standard" chickens). And as speckledhen mentioned, there are some breeds that have a standard and a bantam variety, and some (again, like the seabrights) that are "true bantams" meaning they were not developed from a larger bird and have no large fowl counterpart.
For the most part, folks around here call all little chickens "banties" regardless of breed. (Your local CraigsList ads will give you a pretty good idea of what terms people are using in your area).