Yes, when they're out of diapers it can change, but not enough IMO. It's the main reason I took the seats back. Both of my kids were insanely tight in the crotch, including a skinny 3.5 year old who is long since out of diapers. Here are some pictures of how tight it was on him. He's not even wearing underwear in this pic, just thin flannel pants.
I LOVE the seat, but that is just a horrible design problem IMO. Some kids will fit fine without complaint, it was too tight on him and bruised his thighs from the tightness and angle.
Picture showing how the hip straps went over him. A horrible fit, really, because of how shallow and short that crotch strap is. It was his favorite seat, too.
My younger son was ~2 months at the time, cloth diapered, and with the infant insert I actually could not buckle it. Without the insert, it was tight but doable. He screamed though, and it left horrible marks on his legs.