Yes, the bantams are very small compared to the others of the same age. Probably 1/2 to 1/3 the size. I also saw welsummer as an option? But not sure they come in bantam size.
Welsummers should not have those white feathers, so I'm pretty sure your bantams are not Welsummers. (Welsummer Bantams apparently do exist, because I've seen them listed on at least one hatchery website.)