Yesterday was our BIG DAY. 2 of our 9 hens laid their first egg yesterdat. Today one of the same hens laid another egg and it was noticeably bigger (although still very small for a red sex link) and slightly different coloration. We watched her lay em. Give em a month and you'll see the difference.
They gradually get bigger. Takes about a month or so for them to start laying "full size" eggs, but they really never seem stop getting bigger it just slows down considerably by about 3 months. My oldest hens usually lay the biggest eggs though.
Also some breeds just lay bigger eggs than others (Buff Orpingtons and Leghorns come to mind)
Mine have been laying for 2 months now. They aren't as small as they started out, but they are still the size of a large store-bought egg if not a little smaller. I figured I would be getting huge eggs now but not really.
I have 4 red sex links and I'm sure they are the ones that have been laying. The others are RIRs (4) and black sex links (2). One of the first eggs, which was unfortunately broken
Enjoy your little eggs! My new girls just started laying, and I have a dozen little eggs in the back of the fridge that I am going to make bite sized deviled eggs out of!