I will take a pic of my two week old guppy fry for u when I have a min. They do vary in sizes as they grow. My guess is the females grow larger than the males most often for me anyways so I've always just put it to that, and the fact that all fish differ in size slightly.
I feed three small feeds a day and water change every two days.
I keep the fry with nothing other than a few ghost shrimp I breed also. Then I eventually sell them off or feed them to my angelfish as you get over run with them eventually.
Best of luck with your little ones and i will get u a pic ASAP