I've seen alot of small fawns over the years - even late in the season. I also think it has to do with the amount of does, and some of them getting bred really late. A few years ago on valentines day, I saw a doe standing for a buck in a wide open field. That makes for some really small fawns in the fall.
Oh, and btw...a "yearling" is not a fawn. Yearlings are your 1.5yr old deer.