Apparently a fawn became separated from its mother and decided to hang out with a few horses for safety. The email these came with pointed out that the doe collected her fawn once the horses moved on.
Yes, that little thing near the horse's head is a tiny little deer, maybe a week old at most. She's pretty safe with horses though, they'll tend to be careful around small things and try not to step on them or kick them. Here are a few more shots: