You can get a good idea visually at that size but there are exceptions. I have seen many different adults and some know males look like females and know females look like males visually speaking. Obviously sex is know because they're proven breeders but just goes to show with this species there is no guarantee unless they're proven breeders or scoped to determine sex.
I think I might have one male and the other female, why?
Male-1.15kgs and 7" plastron
Slight concave plastron, more open anal notch and slightly longer gular scutes, stubby tail
Female-1.15kgs and 7.5" plastron
Totally flat plastron, more closed pointed 'v' shape anal notch with hardly developed gular scutes, stubby tail
I know it's a bit early to tell if male or female but I can see where one showing signs of being male, who knows, we'll have to wait till their about 11" just to be sure.