How to Tell the Boys from the Girls
Many people claim that it is hard to sex rabbits (i.e. determine if they are boys or girls), but it's really not, once you get the hang of it. The bunnies in these pictures are barely 3 weeks old.
How To Hold a Bunny to Determine its Sex
Hold the bunny gently, and turn it over on its back so that its body is cradled in your left arm (right arm if you are left-handed), with its head tucked under your arm and its bum resting in your hand.
From there you can expose the genitals as shown in the pictures. Be sure to be gentle as you can injure them if you are not careful.
Apply gentle pressure to the vent area to expose the genitals.
Boys
The boys will have a round opening. When they are a little older, the penis will be clearly visible. It is curved and tapers towards the end. Also when the boys are a little older (depending on breed, 3-4 months and up) there should be 2 clearly visible testicles. They are usually gray or pink and lie on either side of the the vent opening.