Is one a Roo?

So.. I got them thinking they were ISA Reds, however.. I think that they are white laced red bantams? They are pretty small, even smaller than some of my chicks that are a couple weeks younger than them. But is the darker one a roo? I also have 3 white leghorns who I got at the same time, and they are double their size if not bigger.. and the white leghorn roo who is the same age noticeably looks like one and has been crowing for a weeks now