I agree with ronott1, it's hard to tell gender until they are much older. Before then it's really just guesses.
In my stock the girls are much more likely to be vaulted than the boys. If they came from a line where there were lots of other chicks that had vaults I would lean towards boys since they are non vaulted. If not then the vaulted vs non really wont help in determining gender.
The one with the comb has a different type of comb than the one without. Because of this unfortunately you won't be able to compare combs very well to try to determine gender. I suspect your little one with the comb has either a pea or a single or a sort of mix of both (I've seen the weird single/pea on some silkie chicks I've hatched, not sure why the pea wouldn't be completely dominant over the single but it appears to happen sometimes).
The one without the comb has a regular silkie comb. With these combs sometimes the width of the comb can give you a hint into what sex it might be but without having others from the same stock that have the same type of comb it's hard to judge. Just from looking at it I'd say it's not wide enough to be obviously pointing towards a male but just wide enough I'd lean slightly more towards male. Really either one could go either way at this point still though.
Sometimes you'll get early developers. You may see early comb development that will point towards male or even early crowers. More often than not though you'll have to wait a while. By 12 or so weeks having streamers or not will come into the equation of trying to determine gender (some lines you'll have to wait longer but in my hatches from over 8 different breeders usually by 12 weeks streamers would start showing up in the boys). Often by this time combs will be somewhat more developed in males as well.
I've had early developers start getting their combs as early as 3 weeks and I've caught a few little males crowing before reaching a week old (doesn't exactly sound like crowing more like an odd trill when they are that young but the motion looks like the same thing a mature rooster does). Those are more the exceptions though not the norm.
Crowing means it's probably a male but not necessarily guaranteed. I have yet to have a female crow but I've definitely heard of it from others.
Behavior can be somewhat helpful in determining gender but I've had enough females acting more like males and vice versa to not judge too much just based on behavior. Chest bumping, running up to your hand, standing taller, and sparing with other chicks are all more common in male chicks but can happen in females as well. Some of my most aggressive chicks actually turned out female.
Adorable babies by the way!
