To avoid this possible 'mix up' please make sure to use something like small coloured zip ties. You can replace them every week as they grow. That way you know for sure who is whom.
I will be getting bands this week hopefully. At the moment they have a drop of food colouring on their leg feathers.
I had a look at that chick in question and I'm now very on the fence.
My "guesses" at the moment are. Pullet, roo, pullet, roo, Roo???unsure of Pookie (5th chook), pullet and roo. Some of them have developed wattles, so I'm pretty sure about 4 and 7 being roos. I'm also nearly certain 6 is a pullet.
Anyone have more ideas about Emu? Aka first chick
Also consider voice and behavior when startled. One sex may be very consistent with a deeper cackle and stand up more. Also compare foot size. With mine where I have a sex-linked down difference and coloration of exposed areas, I also see something with foot size that is also very different with adults. Not spurs.