It would be very uncommon but not unheard of for a fox to take down a heathy fawn being as the fawn would be larger than a fox's normal prey, also the mother would put a hurting on a fox very quickly if it was going after her baby.
That being said if the fawn was very small and sick and the mother wasn't present it's very possible.
All Garrett: Ace 250 (two), AceApex, VX-9. Have owned just about every Garrett ever made. First three detecter I made myself, with the first one in 1962.
I live on the NW edge of Roswell, NM. There are a pair of fox living under my neighbor's shed. They come over to my place quite often, assuringly to hunt for mice. They're the gray variety, and are friendly enough to almost let you pet them. I don't mind, as I haven't seen a field mouse for several years.