Thats an old wives tale with the legs. Best bet is feather sexing withing the first few days, buying sex link chicks, or having the hatcher vent sex them. Just google feather sexing to get pics to show the difference between the feathers.
i tired this! according to the wise tale i had a girl! well it was NO girl! its just a tale, trust me.... it said mine was a girl by the way it held its legs, turns out i had a cockerel! ! ! old wise tales are fun but don't read too much into them because it just doesn't really work. at least in my case it didnt and i pulled all the old wise tale tricks all coming up female like toe size, third and first, and the hat trick, throwing a hat and seeing who hides, ect ect. in the long run i still ended up with a cockerel, that all the wise tales said was female.: ) so don't put much credit in them. they are fun but not accurate .
With our Wyandotte chicks who were about two weeks old (if I remember their age correctly) we looked at how fast they were feathering. The quicker they were feathering they were girls. My husband tied tie straps loosely around the boys. They had very short tail feathers at the time. The ones with the tie straps are starting to get bigger combs and waddles now. They are about six weeks old now. Females feather faster from what I have learned.