Slight correction. Males don't have seeds - males have little balls. Those balls be the pollen sacks. Females produce seeds when they've been fucked by the yellow dust released from inside those pollen sacks once they pop open.
To sex - after they show a few nodes, you could temporarily flip to 12/12 and after a couple of days, check for any white pistils. If you can see them little white hairs poking out, you've got a female. Congrats!! You can go back to your veg cycle and grow her out.
If you can see those dreaded pollen sacks forming, sadly it's a dude and needs to be culled.