Male or female mallards?

[The Duck Dad]

So I have has these ducklings for about three weeks and am still wondering what gender they are. So the first one has the lighter head stripe and the other two pics are the duckling with the dark stripe, so what I found on google is that the males have the darker stripe? it is just confusing for me when telling the difference. can you guys help? Thanks!

 

[The Moonshiner]

Earliest way I found to accurately sex mallards is to watch the bills. The males will turn green and the females will be a two tone brown and orangish.

 

[JedJackson]

Yep, I noticed the same thing as Moonshiner with mallard bills.