How do I sex Yellow Gouldians?

[Lonchura]

My seven year old daughter has just come home with five yellow Gouldian’s. I can't tell what sex they are! Two have white breasts and white heads the third has a bright Red head and a purple breast the same colour as a female normal. The forth has a black head and a purple breast like a normal male but it has a black beak. The fifth one has a Yellow/Orange head with the same colour breast as a female the previous mentioned red head

[TheFinchMan101]

Yeah it can be hard to tell the yellows apart especially the white breast white head ones, but if you watch carefully you should notice that the males will start singing which would be one way of finding out what sex they are, or you could always post some photos up of them then I'd be able to tell them apart easier if you could do that.

[AMCA26]

In the WB the cock will be more brighter in the yellow of the belly.

[Lonchura]

Thanks everyone!
I will try to post some photos, when I get a chance.