o kay, pick them up in your hand, flip them over, head toward you tail away, Gently fold the tail downward.
Now with your thumbs and index fingers, gently move the fuzz away from the vent, one you've found it, keep the tail downward, and open the vent with your thumbs. Just easily spread it open. Look VERY close. will just be skin is it's a hen, if your boy is still there, you'll see a tiny little pee pee pop out of it, just a very small worm looking think at this point.
That's the only way you'll know at this point, there are no reliable markers on them at this age. This is painless to the bird and does not harm them at all. You may have to try it a few times, but it works, that's how the hatchery sexed them when they sent them to you.