How old are my chicks? Is there a way to tell?

Hi all,

I got some chicks (and their moms) and they are probably somewhere in the 3 to 6 week old range. Is there a place that shows chick pictures so that I can narrow down their ages a bit? I'm curious about them because I want to know when they might start to lay so I can be prepared, and if I don't know how old they are now, I won't know when they are 22 weeks or whatever.

Thanks for any help!
Claire