As with most baby animals, it can be quite difficult to tell the difference between a male and female deer. Identifying the gender of a deer or other baby animal is called "sexing." If there is a group of young deer, you may surmise that the larger ones are males. Otherwise, there are a few other identifiers to looked for. Most young deer are referred to as fawns; however, young sika and red deer are referred to as calves. Baby roe deer are identified as kids.
Look for the hair-covered penis sheath. These are only present in male deer and can appear at a young age. It is a small tuft of hair that hangs down between the two hind legs. This may not be present in a newborn, but it will become more apparent as the deer grows.
Look for antler pedicles. The pedicle is a small growth that will eventually grow into a full-sized antler and is also only present on males. These are located just above the eyes. In a baby, there will be no antler formed yet, but if you can get near enough to the deer to rub its head, look for the small nub of tissue growing in this location. These are present in some older females, but not in younger ones.
Identify if the deer is a roe deer. If it is a roe deer, look for a small tuft of hair just at the base of the rump. This tuft is only present on female roe deer.