Did you know it's possible to sex bunnies soon after they're born? The bunnies in these photos are four days old, but I was able to discern their gender at just one day old. Occasionally it's hard to know, but most of the time you can tell, especially if you have some of each sex to compare to each other.
You can't see the sex organs at this age. All you see are two bulges, one above the other. the top bulge has a dot (urethral opening) and the bottom bulge has a larger hole (anus). The anus is in the same spot in both males and females, but the urethral opening is much closer to the anus in females than it is in males. The urethral opening looks like a dot.
If you look at the two pictures of these four-day-old kits, can you tell which is the male and which is the female? The key is to look at the distance between the anal opening and the urethral (pee) opening.
If you guessed the first is female and the second is male, you are correct! See the larger distance between the openings in the second photograph? In the top photograph, the female urethral opening is very close to the bottom of her vulva, almost looking down toward the anal opening, whereas the male urethral opening is closer to the center and almost looks straight out.
Here are some more photos of the same bunnies:
Again, the top photo is the female, and the bottom is the male.
There are lots of pictures and videos on the internet that can help you sex older bunnies, but not so many that show this type of assessment. I have found this to be more accurate than waiting until they are older. Hope this helps! Good luck!